diff --git a/tools/test_block_removal_parity.py b/tools/test_block_removal_parity.py
index 3185bd4bb3..169806f6ed 100755
--- a/tools/test_block_removal_parity.py
+++ b/tools/test_block_removal_parity.py
@@ -180,9 +180,9 @@ def main():
            '-cp', dependencies, '-d', str(classes), str(java_root / 'dev/horizonlab/parity/VanillaDispenserOracle.java')])
     d.run(['java', '-Xmx3G', '-cp', str(classes) + os.pathsep + dependencies, 'dev.horizonlab.parity.VanillaDispenserOracle',
            str(resources), str(work / 'cases.jsonl'), str(work / 'native.txt')])
-    d.run(['cargo', 'build', '-q', '--release', '-p', 'horizon-client', '--bin', 'horizon-client'], cwd=lab.ROOT,
+    d.run(['cargo', 'build', '-q', '--profile', 'fast', '-p', 'horizon-client', '--bin', 'horizon-client'], cwd=lab.ROOT,
           env={**os.environ, 'CARGO_BUILD_JOBS': os.environ.get('CARGO_BUILD_JOBS', '3')})
-    d.run([str(lab.cargo_target() / 'release/horizon-client'), '--resources', str(resources)], cwd=work,
+    d.run([str(lab.cargo_target() / 'fast/horizon-client'), '--resources', str(resources)], cwd=work,
           env=lab.game_env(HORIZON_DISPENSE_FIXTURE=f'{work / "cases.jsonl"},{work / "rust.txt"}'))
     # Loot table names (D) are vanilla's bookkeeping; the drops themselves are compared.
     ignore = tuple(prefix + ' ' for prefix in args.ignore.split(',') if prefix) + ('D ',)
diff --git a/tools/test_command_exec_parity.py b/tools/test_command_exec_parity.py
index 7993a93a7e..230e72890f 100644
--- a/tools/test_command_exec_parity.py
+++ b/tools/test_command_exec_parity.py
@@ -79,9 +79,9 @@ def main():
     run(['java', '-Xmx3G', '-Duser.timezone=UTC', '-cp', os.pathsep.join([str(classes), str(jars['server']), dependency_path]),
          'dev.horizonlab.parity.VanillaCommandExecOracle', vanilla_dir / 'universe', script_path, build / 'vanilla.jsonl', SEED], 'java', cwd=vanilla_dir)
 
-    run(['cargo', 'build', '--release', '-p', 'horizon-client', '--bin', 'horizon-client'], 'compile-rust', cwd=lab.ROOT)
+    run(['cargo', 'build', '--profile', 'fast', '-p', 'horizon-client', '--bin', 'horizon-client'], 'compile-rust', cwd=lab.ROOT)
     metadata = json.loads(subprocess.check_output(['cargo', 'metadata', '--no-deps', '--format-version', '1'], cwd=lab.ROOT, text=True))
-    binary = Path(metadata['target_directory']) / 'release' / ('horizon-client.exe' if os.name == 'nt' else 'horizon-client')
+    binary = Path(metadata['target_directory']) / 'fast' / ('horizon-client.exe' if os.name == 'nt' else 'horizon-client')
     rust_dir = build / 'rust'
     shutil.rmtree(rust_dir, ignore_errors=True)
     rust_dir.mkdir()
diff --git a/tools/test_command_parse_parity.py b/tools/test_command_parse_parity.py
index 620fb548de..8d8007d0d3 100644
--- a/tools/test_command_parse_parity.py
+++ b/tools/test_command_parse_parity.py
@@ -64,9 +64,9 @@ def main():
     registries = json.loads((build / 'registries.json').read_text())
     corpus = corpus_module.corpus(tree, registries)
     (build / 'corpus.txt').write_text(''.join(line + '\n' for line in corpus), encoding='utf-8')
-    run(['cargo', 'build', '--release', '-p', 'horizon-client', '--example', 'client_probe'], 'compile-rust')
+    run(['cargo', 'build', '--profile', 'fast', '-p', 'horizon-client', '--example', 'client_probe'], 'compile-rust')
     metadata = json.loads(subprocess.check_output(['cargo', 'metadata', '--no-deps', '--format-version', '1'], cwd=lab.ROOT, text=True))
-    binary = Path(metadata['target_directory']) / 'release/examples' / ('client_probe.exe' if os.name=='nt' else 'client_probe')
+    binary = Path(metadata['target_directory']) / 'fast/examples' / ('client_probe.exe' if os.name=='nt' else 'client_probe')
     resources = lab.RESOURCES
     total_failures = 0
     summary = []
diff --git a/tools/test_composter_parity.py b/tools/test_composter_parity.py
index 074b227a89..83b99e9b52 100644
--- a/tools/test_composter_parity.py
+++ b/tools/test_composter_parity.py
@@ -122,9 +122,9 @@ def main():
            '-cp', dependencies, '-d', str(classes), str(java_root / 'dev/horizonlab/parity/VanillaDispenserOracle.java')])
     d.run(['java', '-Xmx3G', '-cp', str(classes) + os.pathsep + dependencies, 'dev.horizonlab.parity.VanillaDispenserOracle',
            str(resources), str(work / 'cases.jsonl'), str(work / 'native.txt')])
-    d.run(['cargo', 'build', '-q', '--release', '-p', 'horizon-client', '--bin', 'horizon-client'], cwd=lab.ROOT,
+    d.run(['cargo', 'build', '-q', '--profile', 'fast', '-p', 'horizon-client', '--bin', 'horizon-client'], cwd=lab.ROOT,
           env={**os.environ, 'CARGO_BUILD_JOBS': os.environ.get('CARGO_BUILD_JOBS', '3')})
-    d.run([str(lab.cargo_target() / 'release/horizon-client'), '--resources', str(resources)], cwd=work,
+    d.run([str(lab.cargo_target() / 'fast/horizon-client'), '--resources', str(resources)], cwd=work,
           env=lab.game_env(HORIZON_DISPENSE_FIXTURE=f'{work / "cases.jsonl"},{work / "rust.txt"}'))
     ignore = tuple(prefix + ' ' for prefix in args.ignore.split(',') if prefix) + ('D ',)
     native = h.split_cases((work / 'native.txt').read_text(), ignore)
diff --git a/tools/test_crafter_parity.py b/tools/test_crafter_parity.py
index b9c343d4db..dcb5cd127c 100644
--- a/tools/test_crafter_parity.py
+++ b/tools/test_crafter_parity.py
@@ -242,9 +242,9 @@ def main():
            '-cp', dependencies, '-d', str(classes), str(java_root / 'dev/horizonlab/parity/VanillaDispenserOracle.java')])
     d.run(['java', '-Xmx3G', '-cp', str(classes) + os.pathsep + dependencies, 'dev.horizonlab.parity.VanillaDispenserOracle',
            str(resources), str(work / 'cases.jsonl'), str(work / 'native.txt')])
-    d.run(['cargo', 'build', '-q', '--release', '-p', 'horizon-client', '--bin', 'horizon-client'], cwd=lab.ROOT,
+    d.run(['cargo', 'build', '-q', '--profile', 'fast', '-p', 'horizon-client', '--bin', 'horizon-client'], cwd=lab.ROOT,
           env={**os.environ, 'CARGO_BUILD_JOBS': os.environ.get('CARGO_BUILD_JOBS', '3')})
-    d.run([str(lab.cargo_target() / 'release/horizon-client'), '--resources', str(resources)], cwd=work,
+    d.run([str(lab.cargo_target() / 'fast/horizon-client'), '--resources', str(resources)], cwd=work,
           env=lab.game_env(HORIZON_DISPENSE_FIXTURE=f'{work / "cases.jsonl"},{work / "rust.txt"}'))
     ignore = tuple(prefix + ' ' for prefix in args.ignore.split(',') if prefix) + ('D ',)
     native = h.split_cases((work / 'native.txt').read_text(), ignore)
diff --git a/tools/test_dedicated_server_parity.py b/tools/test_dedicated_server_parity.py
index 7572ee3e21..9d7080c7f1 100644
--- a/tools/test_dedicated_server_parity.py
+++ b/tools/test_dedicated_server_parity.py
@@ -424,11 +424,11 @@ def main():
     oh.run_logged(['javac', '--release', lock['minecraft']['java_major'], '-proc:none', '-nowarn', '-sourcepath',
                    lab.ROOT / 'mods/horizon/src/test/java', '-cp', dependencies, '-d', classes, oracle],
                   build, 'compile-java')
-    oh.run_logged(['cargo', 'build', '--release', '-p', 'horizon-client', '--bin', 'horizon-client'], build,
+    oh.run_logged(['cargo', 'build', '--profile', 'fast', '-p', 'horizon-client', '--bin', 'horizon-client'], build,
                   'compile-rust')
     metadata = json.loads(subprocess.check_output(['cargo', 'metadata', '--no-deps', '--format-version', '1'],
                                                   cwd=lab.ROOT, text=True))
-    binary = Path(metadata['target_directory']) / 'release' / ('horizon-client.exe' if os.name == 'nt' else 'horizon-client')
+    binary = Path(metadata['target_directory']) / 'fast' / ('horizon-client.exe' if os.name == 'nt' else 'horizon-client')
     vanilla_server = ['java', '-Xmx2g', '-Duser.timezone=UTC', '-cp', dependencies, 'net.minecraft.server.Main', 'nogui']
     horizon_server = [binary, '--resources', lab.RESOURCES, '--dedicated', '--nogui']
 
diff --git a/tools/test_dispenser_parity.py b/tools/test_dispenser_parity.py
index a2c6ba036d..729d8e8b7a 100644
--- a/tools/test_dispenser_parity.py
+++ b/tools/test_dispenser_parity.py
@@ -417,9 +417,9 @@ def main():
          '-cp', dependencies, '-d', str(classes), str(java_root / 'dev/horizonlab/parity/VanillaDispenserOracle.java')])
     run(['java', '-Xmx3G', '-cp', str(classes) + os.pathsep + dependencies, 'dev.horizonlab.parity.VanillaDispenserOracle',
          str(resources), str(work / 'cases.jsonl'), str(work / 'native.txt')])
-    run(['cargo', 'build', '-q', '--release', '-p', 'horizon-client', '--bin', 'horizon-client'], cwd=lab.ROOT,
+    run(['cargo', 'build', '-q', '--profile', 'fast', '-p', 'horizon-client', '--bin', 'horizon-client'], cwd=lab.ROOT,
         env={**os.environ, 'CARGO_BUILD_JOBS': os.environ.get('CARGO_BUILD_JOBS', '3')})
-    run([str(lab.cargo_target() / 'release/horizon-client'), '--resources', str(resources)], cwd=work,
+    run([str(lab.cargo_target() / 'fast/horizon-client'), '--resources', str(resources)], cwd=work,
         env=lab.game_env(HORIZON_DISPENSE_FIXTURE=f'{work / "cases.jsonl"},{work / "rust.txt"}'))
     # Loot table names (D) are vanilla's bookkeeping; the drops themselves are compared.
     ignore = tuple(prefix + ' ' for prefix in args.ignore.split(',') if prefix) + ('D ',)
diff --git a/tools/test_enchanting_parity.py b/tools/test_enchanting_parity.py
index 35f0777c89..9e070c3cbf 100644
--- a/tools/test_enchanting_parity.py
+++ b/tools/test_enchanting_parity.py
@@ -56,9 +56,9 @@ def main():
         with (build / (name + '.log')).open('w', encoding='utf-8') as log:
             base.run(list(map(str, command)), stdout=log, stderr=subprocess.STDOUT)
     run(['javac', '--release', lock['minecraft']['java_major'], '-proc:none','-sourcepath',str(lab.ROOT/'mods/horizon/src/test/java'), '-cp', str(jars['server']) + os.pathsep + deps, '-d', classes, oracle], 'compile-java')
-    run(['cargo', 'build', '--release', '-p', 'horizon-client', '--example', 'client_probe'], 'compile-rust')
+    run(['cargo', 'build', '--profile', 'fast', '-p', 'horizon-client', '--example', 'client_probe'], 'compile-rust')
     metadata = json.loads(subprocess.check_output(['cargo', 'metadata', '--no-deps', '--format-version', '1'], cwd=lab.ROOT, text=True))
-    binary = Path(metadata['target_directory']) / 'release/examples' / ('client_probe.exe' if os.name=='nt' else 'client_probe')
+    binary = Path(metadata['target_directory']) / 'fast/examples' / ('client_probe.exe' if os.name=='nt' else 'client_probe')
     run([binary, 'enchanting_fixture',resources, inputs, build / 'rust.txt'], 'rust')
     references = []
     for side in ['server']:
diff --git a/tools/test_entity_death_loot_parity.py b/tools/test_entity_death_loot_parity.py
index 07c77b0b81..2bb53ebbbb 100644
--- a/tools/test_entity_death_loot_parity.py
+++ b/tools/test_entity_death_loot_parity.py
@@ -139,9 +139,9 @@ def main():
          '-cp', str(jars['server']) + os.pathsep + deps, '-d', classes, oracle], 'compile-java')
     run(['java', '-Xmx2G', '-cp', os.pathsep.join([str(classes), str(jars['server']), deps]),
          'dev.horizonlab.parity.VanillaEntityDeathLootOracle', inputs, build / 'server.txt'], 'server')
-    run(['cargo', 'build', '--release', '-p', 'horizon-client', '--example', 'client_probe'], 'compile-rust')
+    run(['cargo', 'build', '--profile', 'fast', '-p', 'horizon-client', '--example', 'client_probe'], 'compile-rust')
     metadata = json.loads(subprocess.check_output(['cargo', 'metadata', '--no-deps', '--format-version', '1'], cwd=lab.ROOT, text=True))
-    binary = Path(metadata['target_directory']) / 'release/examples/client_probe'
+    binary = Path(metadata['target_directory']) / 'fast/examples/client_probe'
     run([binary, 'entity_death_loot_fixture', resources, inputs, build / 'rust.txt'], 'rust')
     errors = [l for l in (build / 'server.txt').read_text().splitlines() if l.startswith('error ')]
     if errors:
diff --git a/tools/test_finalize_spawn_parity.py b/tools/test_finalize_spawn_parity.py
index 7d581fefc0..0e889598c2 100644
--- a/tools/test_finalize_spawn_parity.py
+++ b/tools/test_finalize_spawn_parity.py
@@ -148,9 +148,9 @@ def main():
         print(f'{len(vanilla)} oracle lines')
         return
     halloween = vanilla[0].split()[1]
-    run(['cargo', 'build', '--release', '-p', 'horizon-client', '--example', 'client_probe'], 'compile-rust')
+    run(['cargo', 'build', '--profile', 'fast', '-p', 'horizon-client', '--example', 'client_probe'], 'compile-rust')
     metadata = json.loads(subprocess.check_output(['cargo', 'metadata', '--no-deps', '--format-version', '1'], cwd=lab.ROOT, text=True))
-    binary = Path(metadata['target_directory']) / 'release/examples/client_probe'
+    binary = Path(metadata['target_directory']) / 'fast/examples/client_probe'
     run([binary, 'finalize_spawn_fixture', resources, inputs, build / 'rust.txt', halloween], 'rust')
     rust = (build / 'rust.txt').read_text().splitlines()
     bad = [(a, b) for a, b in zip(vanilla, rust) if a != b]
diff --git a/tools/test_locator_bar_parity.py b/tools/test_locator_bar_parity.py
index 6574af76e6..05f4794617 100644
--- a/tools/test_locator_bar_parity.py
+++ b/tools/test_locator_bar_parity.py
@@ -258,12 +258,12 @@ def sides(name):
     subprocess.run(['javac', '--release', str(lock['minecraft']['java_major']), '-proc:none', '-nowarn', '-sourcepath',
                     lab.ROOT / 'mods/horizon/src/test/java', '-cp', dependencies, '-d', classes, oracle],
                    cwd=lab.ROOT, check=True, capture_output=True)
-    subprocess.run(['cargo', 'build', '--release', '-p', 'horizon-client', '--bin', 'horizon-client'], cwd=lab.ROOT,
+    subprocess.run(['cargo', 'build', '--profile', 'fast', '-p', 'horizon-client', '--bin', 'horizon-client'], cwd=lab.ROOT,
                    check=True, capture_output=True)
     import json
     metadata = json.loads(subprocess.check_output(['cargo', 'metadata', '--no-deps', '--format-version', '1'],
                                                   cwd=lab.ROOT, text=True))
-    binary = Path(metadata['target_directory']) / 'release' / ('horizon-client.exe' if os.name == 'nt' else 'horizon-client')
+    binary = Path(metadata['target_directory']) / 'fast' / ('horizon-client.exe' if os.name == 'nt' else 'horizon-client')
     vanilla_server = ['java', '-Xmx2g', '-Duser.timezone=UTC', '-cp', dependencies, 'net.minecraft.server.Main', 'nogui']
     horizon_server = [binary, '--resources', lab.LOCAL / 'horizon-client/26.3', '--dedicated', '--nogui']
     client = ['java', '-Xmx1g', '-cp', str(classes) + os.pathsep + dependencies, 'dev.horizonlab.parity.LocatorBarClient']
diff --git a/tools/test_mace_parity.py b/tools/test_mace_parity.py
index 578e9e6eeb..2ff560b8d3 100644
--- a/tools/test_mace_parity.py
+++ b/tools/test_mace_parity.py
@@ -167,9 +167,9 @@ def main():
            '-cp', dependencies, '-d', str(classes), str(java_root / 'dev/horizonlab/parity/VanillaDispenserOracle.java')])
     d.run(['java', '-Xmx3G', '-cp', str(classes) + os.pathsep + dependencies, 'dev.horizonlab.parity.VanillaDispenserOracle',
            str(resources), str(work / 'cases.jsonl'), str(work / 'native.txt')])
-    d.run(['cargo', 'build', '-q', '--release', '-p', 'horizon-client', '--bin', 'horizon-client'], cwd=lab.ROOT,
+    d.run(['cargo', 'build', '-q', '--profile', 'fast', '-p', 'horizon-client', '--bin', 'horizon-client'], cwd=lab.ROOT,
           env={**os.environ, 'CARGO_BUILD_JOBS': os.environ.get('CARGO_BUILD_JOBS', '3')})
-    d.run([str(lab.cargo_target() / 'release/horizon-client'), '--resources', str(resources)], cwd=work,
+    d.run([str(lab.cargo_target() / 'fast/horizon-client'), '--resources', str(resources)], cwd=work,
           env=lab.game_env(HORIZON_DISPENSE_FIXTURE=f'{work / "cases.jsonl"},{work / "rust.txt"}'))
     ignore = tuple(prefix + ' ' for prefix in args.ignore.split(',') if prefix) + ('D ',)
     native = h.split_cases((work / 'native.txt').read_text(), ignore)
diff --git a/tools/test_mob_ai_parity.py b/tools/test_mob_ai_parity.py
index 133deca2d9..9d88ca18de 100644
--- a/tools/test_mob_ai_parity.py
+++ b/tools/test_mob_ai_parity.py
@@ -525,7 +525,7 @@ def main():
                                    'dev.horizonlab.parity.VanillaMobAiOracle', inputs, build / 'vanilla.txt', world],
                                   build, 'vanilla', timeout=3600)
     if not args.java_only:
-        command = ['cargo', 'build', '--locked', '--release', '-p', 'horizon-client', '--example', 'client_probe']
+        command = ['cargo', 'build', '--locked', '--profile', 'fast', '-p', 'horizon-client', '--example', 'client_probe']
         target, env = lab.cargo_target(), None
         if args.trace:
             target = lab.LOCAL / 'mob-ai-trace-target'
@@ -533,7 +533,7 @@ def main():
             env = dict(os.environ, CARGO_TARGET_DIR=str(target), CARGO_PROFILE_RELEASE_DEBUG='line-tables-only',
                        CARGO_PROFILE_RELEASE_LTO='false', CARGO_PROFILE_RELEASE_CODEGEN_UNITS='16')
         oracle_harness.run_logged(command, build, 'compile-rust', env=env)
-        binary = target / 'release/examples/client_probe'
+        binary = target / 'fast/examples/client_probe'
         oracle_harness.run_logged([binary, 'mob_ai_probe', lab.RESOURCES, inputs, build / 'horizon.txt'], build, 'horizon')
     if args.java_only:
         return
diff --git a/tools/test_mob_attributes_parity.py b/tools/test_mob_attributes_parity.py
index 7fa1df5e61..27f2b238b5 100755
--- a/tools/test_mob_attributes_parity.py
+++ b/tools/test_mob_attributes_parity.py
@@ -62,8 +62,8 @@ def main():
             subprocess.run(list(map(str, cmd)), cwd=lab.ROOT, check=True, timeout=3600, stdout=log, stderr=subprocess.STDOUT)
     run(['javac', '--release', lock['minecraft']['java_major'], '-proc:none', '-cp', str(jars['server']) + os.pathsep + deps, '-d', classes, oracle], 'compile-java')
     run(['java', '-Xmx1G', '-cp', os.pathsep.join([str(classes), str(jars['server']), deps]), 'dev.horizonlab.parity.VanillaMobAttributesOracle', build / 'vanilla.txt'], 'java')
-    run(['cargo', 'build', '--release', '-p', 'horizon-client', '--example', 'client_probe'], 'compile-rust')
-    binary = lab.cargo_target() / 'release/examples/client_probe'
+    run(['cargo', 'build', '--profile', 'fast', '-p', 'horizon-client', '--example', 'client_probe'], 'compile-rust')
+    binary = lab.cargo_target() / 'fast/examples/client_probe'
     resources = lab.RESOURCES
     run([binary, 'mob_attributes_fixture', resources, build / 'rust.txt'], 'rust')
     vanilla, rust = parse(build / 'vanilla.txt'), parse(build / 'rust.txt')
diff --git a/tools/test_natural_spawn_parity.py b/tools/test_natural_spawn_parity.py
index 50781eca7f..bd3eb2540d 100644
--- a/tools/test_natural_spawn_parity.py
+++ b/tools/test_natural_spawn_parity.py
@@ -568,9 +568,9 @@ def main():
          '-cp', str(jars['server']) + os.pathsep + deps, '-d', classes, oracle], 'compile-java')
     run(['java', '-Xmx3G', '-cp', os.pathsep.join([str(classes), str(jars['server']), deps]),
          'dev.horizonlab.parity.VanillaNaturalSpawnOracle', inputs, build / 'server.txt'], 'server')
-    run(['cargo', 'build', '--release', '-p', 'horizon-client', '--example', 'client_probe'], 'compile-rust')
+    run(['cargo', 'build', '--profile', 'fast', '-p', 'horizon-client', '--example', 'client_probe'], 'compile-rust')
     metadata = json.loads(subprocess.check_output(['cargo', 'metadata', '--no-deps', '--format-version', '1'], cwd=lab.ROOT, text=True))
-    binary = Path(metadata['target_directory']) / 'release/examples/client_probe'
+    binary = Path(metadata['target_directory']) / 'fast/examples/client_probe'
     run([binary, 'natural_spawn_fixture', resources, inputs, build / 'rust.txt'], 'rust')
     vanilla = (build / 'server.txt').read_text().splitlines()
     errors = [l for l in vanilla if ' error ' in l]
diff --git a/tools/test_online_mode_parity.py b/tools/test_online_mode_parity.py
index 8096efd800..0025168960 100644
--- a/tools/test_online_mode_parity.py
+++ b/tools/test_online_mode_parity.py
@@ -351,11 +351,11 @@ def main():
     build.mkdir(parents=True, exist_ok=True)
     report = build / 'report.json'
     report.unlink(missing_ok=True)
-    oh.run_logged(['cargo', 'build', '--release', '-p', 'horizon-client', '--bin', 'horizon-client'], build,
+    oh.run_logged(['cargo', 'build', '--profile', 'fast', '-p', 'horizon-client', '--bin', 'horizon-client'], build,
                   'compile-rust')
     metadata = json.loads(subprocess.check_output(['cargo', 'metadata', '--no-deps', '--format-version', '1'],
                                                   cwd=lab.ROOT, text=True))
-    binary = Path(metadata['target_directory']) / 'release' / ('horizon-client.exe' if os.name == 'nt' else 'horizon-client')
+    binary = Path(metadata['target_directory']) / 'fast' / ('horizon-client.exe' if os.name == 'nt' else 'horizon-client')
     dependencies = os.pathsep.join(map(str, [jars['server'], *libraries]))
 
     services = Services()
diff --git a/tools/test_raid_parity.py b/tools/test_raid_parity.py
index 4928c9715e..6beadf52b9 100644
--- a/tools/test_raid_parity.py
+++ b/tools/test_raid_parity.py
@@ -335,9 +335,9 @@ def main():
          '-cp', str(jars['server']) + os.pathsep + deps, '-d', classes, oracle], 'compile-java')
     run(['java', '-Xmx3G', '-cp', os.pathsep.join([str(classes), str(jars['server']), deps]),
          'dev.horizonlab.parity.VanillaRaidOracle', inputs, build / 'server.txt'], 'server')
-    run(['cargo', 'build', '--release', '-p', 'horizon-client', '--example', 'client_probe'], 'compile-rust')
+    run(['cargo', 'build', '--profile', 'fast', '-p', 'horizon-client', '--example', 'client_probe'], 'compile-rust')
     metadata = json.loads(subprocess.check_output(['cargo', 'metadata', '--no-deps', '--format-version', '1'], cwd=lab.ROOT, text=True))
-    binary = Path(metadata['target_directory']) / 'release/examples/client_probe'
+    binary = Path(metadata['target_directory']) / 'fast/examples/client_probe'
     run([binary, 'raid_fixture', resources, inputs, build / 'rust.txt'], 'rust')
     vanilla = (build / 'server.txt').read_text().splitlines()
     errors = [l for l in vanilla if ' error ' in l]
diff --git a/tools/test_scoreboard_parity.py b/tools/test_scoreboard_parity.py
index b38dfb3015..8098ae681a 100644
--- a/tools/test_scoreboard_parity.py
+++ b/tools/test_scoreboard_parity.py
@@ -250,9 +250,9 @@ def main():
     inputs = build / 'inputs.jsonl'
     inputs.write_text(''.join(json.dumps(c, ensure_ascii=False) + '\n' for c in chosen), encoding='utf-8')
     run([*oracle, 'run', inputs, build / 'vanilla.jsonl'], 'vanilla')
-    run(['cargo', 'build', '--release', '-p', 'horizon-client', '--example', 'client_probe'], 'compile-rust')
+    run(['cargo', 'build', '--profile', 'fast', '-p', 'horizon-client', '--example', 'client_probe'], 'compile-rust')
     metadata = json.loads(subprocess.check_output(['cargo', 'metadata', '--no-deps', '--format-version', '1'], cwd=lab.ROOT, text=True))
-    binary = Path(metadata['target_directory']) / 'release/examples' / ('client_probe.exe' if os.name=='nt' else 'client_probe')
+    binary = Path(metadata['target_directory']) / 'fast/examples' / ('client_probe.exe' if os.name=='nt' else 'client_probe')
     run([binary, 'scoreboard_fixture',build / 'registries.json', inputs, build / 'rust.jsonl', build / 'vanilla.jsonl'], 'rust')
     read = lambda p: [json.loads(l) for l in p.read_text(encoding='utf-8').splitlines()]
     vanilla, rust = read(build / 'vanilla.jsonl'), read(build / 'rust.jsonl')
diff --git a/tools/test_sculk_parity.py b/tools/test_sculk_parity.py
index bff5ad5ba9..b4195e5c33 100644
--- a/tools/test_sculk_parity.py
+++ b/tools/test_sculk_parity.py
@@ -336,9 +336,9 @@ def main():
                                    'dev.horizonlab.parity.VanillaSculkOracle', inputs, build / 'vanilla.txt'],
                                   build, 'vanilla', timeout=3600)
     if not args.java_only:
-        oracle_harness.run_logged(['cargo', 'build', '--locked', '--release', '-p', 'horizon-client', '--bin', 'horizon-client'],
+        oracle_harness.run_logged(['cargo', 'build', '--locked', '--profile', 'fast', '-p', 'horizon-client', '--bin', 'horizon-client'],
                                   build, 'compile-rust')
-        oracle_harness.run_logged([lab.cargo_target() / 'release/horizon-client', '--resources', resources], build, 'horizon',
+        oracle_harness.run_logged([lab.cargo_target() / 'fast/horizon-client', '--resources', resources], build, 'horizon',
                                   env=lab.game_env(HORIZON_SCULK_FIXTURE=f'{inputs},{build / "horizon.txt"}'))
     if args.java_only:
         return
diff --git a/tools/test_secure_chat_parity.py b/tools/test_secure_chat_parity.py
index b9062568a7..a4f77470f6 100644
--- a/tools/test_secure_chat_parity.py
+++ b/tools/test_secure_chat_parity.py
@@ -254,11 +254,11 @@ def main():
     oh.run_logged(['javac', '--release', lock['minecraft']['java_major'], '-proc:none', '-nowarn', '-sourcepath',
                    lab.ROOT / 'mods/horizon/src/test/java', '-cp', dependencies, '-d', classes, oracle],
                   build, 'compile-java')
-    oh.run_logged(['cargo', 'build', '--release', '-p', 'horizon-client', '--bin', 'horizon-client'], build,
+    oh.run_logged(['cargo', 'build', '--profile', 'fast', '-p', 'horizon-client', '--bin', 'horizon-client'], build,
                   'compile-rust')
     metadata = json.loads(subprocess.check_output(['cargo', 'metadata', '--no-deps', '--format-version', '1'],
                                                   cwd=lab.ROOT, text=True))
-    binary = Path(metadata['target_directory']) / 'release' / ('horizon-client.exe' if os.name == 'nt' else 'horizon-client')
+    binary = Path(metadata['target_directory']) / 'fast' / ('horizon-client.exe' if os.name == 'nt' else 'horizon-client')
     java = ['java', '-Xmx1g', '-Duser.timezone=UTC', '-cp', str(classes) + os.pathsep + dependencies,
             'dev.horizonlab.parity.SecureChatClient']
     oh.run_logged([*java, 'keys', build], build, 'keys')
diff --git a/tools/test_server_dimension_players_parity.py b/tools/test_server_dimension_players_parity.py
index ea026a5093..887ebb2d7d 100644
--- a/tools/test_server_dimension_players_parity.py
+++ b/tools/test_server_dimension_players_parity.py
@@ -118,12 +118,12 @@ def main():
     subprocess.run(['javac', '--release', str(lock['minecraft']['java_major']), '-proc:none', '-nowarn', '-sourcepath',
                     lab.ROOT / 'mods/horizon/src/test/java', '-cp', dependencies, '-d', classes, oracle],
                    cwd=lab.ROOT, check=True, capture_output=True)
-    subprocess.run(['cargo', 'build', '--release', '-p', 'horizon-client', '--bin', 'horizon-client'], cwd=lab.ROOT,
+    subprocess.run(['cargo', 'build', '--profile', 'fast', '-p', 'horizon-client', '--bin', 'horizon-client'], cwd=lab.ROOT,
                    check=True, capture_output=True)
     import json
     metadata = json.loads(subprocess.check_output(['cargo', 'metadata', '--no-deps', '--format-version', '1'],
                                                   cwd=lab.ROOT, text=True))
-    binary = Path(metadata['target_directory']) / 'release' / ('horizon-client.exe' if os.name == 'nt' else 'horizon-client')
+    binary = Path(metadata['target_directory']) / 'fast' / ('horizon-client.exe' if os.name == 'nt' else 'horizon-client')
     vanilla_server = ['java', '-Xmx2g', '-Duser.timezone=UTC', '-cp', dependencies, 'net.minecraft.server.Main', 'nogui']
     horizon_server = [binary, '--resources', lab.LOCAL / 'horizon-client/26.3', '--dedicated', '--nogui']
     client = ['java', '-Xmx1g', '-cp', str(classes) + os.pathsep + dependencies, 'dev.horizonlab.parity.LocatorBarClient']
diff --git a/tools/test_server_dragon_parity.py b/tools/test_server_dragon_parity.py
index dc58e851dc..563ac788a2 100644
--- a/tools/test_server_dragon_parity.py
+++ b/tools/test_server_dragon_parity.py
@@ -101,12 +101,12 @@ def main():
     # SERVER_DRAGON_SIDES=vanilla (or horizon) runs one side and reads the other's last transcript.
     sides = [s for s in os.environ.get('SERVER_DRAGON_SIDES', 'vanilla,horizon').split(',') if s]
     if 'horizon' in sides:
-        subprocess.run(['cargo', 'build', '--release', '-p', 'horizon-client', '--bin', 'horizon-client'], cwd=lab.ROOT,
+        subprocess.run(['cargo', 'build', '--profile', 'fast', '-p', 'horizon-client', '--bin', 'horizon-client'], cwd=lab.ROOT,
                        check=True, capture_output=True)
     import json
     metadata = json.loads(subprocess.check_output(['cargo', 'metadata', '--no-deps', '--format-version', '1'],
                                                   cwd=lab.ROOT, text=True))
-    binary = Path(metadata['target_directory']) / 'release' / ('horizon-client.exe' if os.name == 'nt' else 'horizon-client')
+    binary = Path(metadata['target_directory']) / 'fast' / ('horizon-client.exe' if os.name == 'nt' else 'horizon-client')
     vanilla_server = ['java', '-Xmx2g', '-Duser.timezone=UTC', '-cp', dependencies, 'net.minecraft.server.Main', 'nogui']
     horizon_server = [binary, '--resources', lab.LOCAL / 'horizon-client/26.3', '--dedicated', '--nogui']
     client = ['java', '-Xmx1g', '-Duser.timezone=UTC', '-cp', str(classes) + os.pathsep + dependencies,
diff --git a/tools/test_server_entities_parity.py b/tools/test_server_entities_parity.py
index fba196c72b..b8c5a7defd 100644
--- a/tools/test_server_entities_parity.py
+++ b/tools/test_server_entities_parity.py
@@ -157,12 +157,12 @@ def main():
     # SERVER_ENTITIES_SIDES=vanilla (or horizon) runs one side and reads the other's last transcript.
     sides = [s for s in os.environ.get('SERVER_ENTITIES_SIDES', 'vanilla,horizon').split(',') if s]
     if 'horizon' in sides:
-        subprocess.run(['cargo', 'build', '--release', '-p', 'horizon-client', '--bin', 'horizon-client'], cwd=lab.ROOT,
+        subprocess.run(['cargo', 'build', '--profile', 'fast', '-p', 'horizon-client', '--bin', 'horizon-client'], cwd=lab.ROOT,
                        check=True, capture_output=True)
     import json
     metadata = json.loads(subprocess.check_output(['cargo', 'metadata', '--no-deps', '--format-version', '1'],
                                                   cwd=lab.ROOT, text=True))
-    binary = Path(metadata['target_directory']) / 'release' / ('horizon-client.exe' if os.name == 'nt' else 'horizon-client')
+    binary = Path(metadata['target_directory']) / 'fast' / ('horizon-client.exe' if os.name == 'nt' else 'horizon-client')
     vanilla_server = ['java', '-Xmx2g', '-Duser.timezone=UTC', '-cp', dependencies, 'net.minecraft.server.Main', 'nogui']
     horizon_server = [binary, '--resources', lab.LOCAL / 'horizon-client/26.3', '--dedicated', '--nogui']
     client = ['java', '-Xmx1g', '-Duser.timezone=UTC', '-cp', str(classes) + os.pathsep + dependencies,
diff --git a/tools/test_server_knockback_parity.py b/tools/test_server_knockback_parity.py
index 66b75946e3..b3c4355eaa 100644
--- a/tools/test_server_knockback_parity.py
+++ b/tools/test_server_knockback_parity.py
@@ -334,12 +334,12 @@ def main():
     subprocess.run(['javac', '--release', str(lock['minecraft']['java_major']), '-proc:none', '-nowarn', '-sourcepath',
                     lab.ROOT / 'mods/horizon/src/test/java', '-cp', dependencies, '-d', classes, oracle],
                    cwd=lab.ROOT, check=True, capture_output=True)
-    subprocess.run(['cargo', 'build', '--release', '-p', 'horizon-client', '--bin', 'horizon-client'], cwd=lab.ROOT,
+    subprocess.run(['cargo', 'build', '--profile', 'fast', '-p', 'horizon-client', '--bin', 'horizon-client'], cwd=lab.ROOT,
                    check=True, capture_output=True)
     import json
     metadata = json.loads(subprocess.check_output(['cargo', 'metadata', '--no-deps', '--format-version', '1'],
                                                   cwd=lab.ROOT, text=True))
-    binary = Path(metadata['target_directory']) / 'release' / ('horizon-client.exe' if os.name == 'nt' else 'horizon-client')
+    binary = Path(metadata['target_directory']) / 'fast' / ('horizon-client.exe' if os.name == 'nt' else 'horizon-client')
     vanilla_server = ['java', '-Xmx2g', '-Duser.timezone=UTC', '-cp', dependencies, 'net.minecraft.server.Main', 'nogui']
     horizon_server = [binary, '--resources', lab.LOCAL / 'horizon-client/26.3', '--dedicated', '--nogui']
     client = ['java', '-Xmx1g', '-cp', str(classes) + os.pathsep + dependencies, 'dev.horizonlab.parity.KnockbackClient']
diff --git a/tools/test_server_ops_feedback_parity.py b/tools/test_server_ops_feedback_parity.py
index 91854fac65..eb77885454 100644
--- a/tools/test_server_ops_feedback_parity.py
+++ b/tools/test_server_ops_feedback_parity.py
@@ -118,12 +118,12 @@ def main():
     subprocess.run(['javac', '--release', str(lock['minecraft']['java_major']), '-proc:none', '-nowarn', '-sourcepath',
                     lab.ROOT / 'mods/horizon/src/test/java', '-cp', dependencies, '-d', classes, oracle],
                    cwd=lab.ROOT, check=True, capture_output=True)
-    subprocess.run(['cargo', 'build', '--release', '-p', 'horizon-client', '--bin', 'horizon-client'], cwd=lab.ROOT,
+    subprocess.run(['cargo', 'build', '--profile', 'fast', '-p', 'horizon-client', '--bin', 'horizon-client'], cwd=lab.ROOT,
                    check=True, capture_output=True)
     import json
     metadata = json.loads(subprocess.check_output(['cargo', 'metadata', '--no-deps', '--format-version', '1'],
                                                   cwd=lab.ROOT, text=True))
-    binary = Path(metadata['target_directory']) / 'release' / ('horizon-client.exe' if os.name == 'nt' else 'horizon-client')
+    binary = Path(metadata['target_directory']) / 'fast' / ('horizon-client.exe' if os.name == 'nt' else 'horizon-client')
     vanilla_server = ['java', '-Xmx2g', '-Duser.timezone=UTC', '-cp', dependencies, 'net.minecraft.server.Main', 'nogui']
     horizon_server = [binary, '--resources', lab.LOCAL / 'horizon-client/26.3', '--dedicated', '--nogui']
     client = ['java', '-Xmx1g', '-cp', str(classes) + os.pathsep + dependencies, 'dev.horizonlab.parity.LocatorBarClient']
diff --git a/tools/test_server_player_targets_parity.py b/tools/test_server_player_targets_parity.py
index 263aa4a591..321a39f069 100644
--- a/tools/test_server_player_targets_parity.py
+++ b/tools/test_server_player_targets_parity.py
@@ -169,12 +169,12 @@ def main():
     subprocess.run(['javac', '--release', str(lock['minecraft']['java_major']), '-proc:none', '-nowarn', '-sourcepath',
                     lab.ROOT / 'mods/horizon/src/test/java', '-cp', dependencies, '-d', classes, oracle],
                    cwd=lab.ROOT, check=True, capture_output=True)
-    subprocess.run(['cargo', 'build', '--release', '-p', 'horizon-client', '--bin', 'horizon-client'], cwd=lab.ROOT,
+    subprocess.run(['cargo', 'build', '--profile', 'fast', '-p', 'horizon-client', '--bin', 'horizon-client'], cwd=lab.ROOT,
                    check=True, capture_output=True)
     import json
     metadata = json.loads(subprocess.check_output(['cargo', 'metadata', '--no-deps', '--format-version', '1'],
                                                   cwd=lab.ROOT, text=True))
-    binary = Path(metadata['target_directory']) / 'release' / ('horizon-client.exe' if os.name == 'nt' else 'horizon-client')
+    binary = Path(metadata['target_directory']) / 'fast' / ('horizon-client.exe' if os.name == 'nt' else 'horizon-client')
     vanilla_server = ['java', '-Xmx2g', '-Duser.timezone=UTC', '-cp', dependencies, 'net.minecraft.server.Main', 'nogui']
     horizon_server = [binary, '--resources', lab.LOCAL / 'horizon-client/26.3', '--dedicated', '--nogui']
     client = ['java', '-Xmx1g', '-cp', str(classes) + os.pathsep + dependencies, 'dev.horizonlab.parity.LocatorBarClient']
diff --git a/tools/test_server_resource_pack_parity.py b/tools/test_server_resource_pack_parity.py
index 0f5d258c6f..10965d273a 100644
--- a/tools/test_server_resource_pack_parity.py
+++ b/tools/test_server_resource_pack_parity.py
@@ -134,9 +134,9 @@ def main():
     subprocess.run(['javac', '--release', str(lock['minecraft']['java_major']), '-proc:none', '-nowarn', '-sourcepath',
                     lab.ROOT / 'mods/horizon/src/test/java', '-cp', dependencies, '-d', classes, oracle],
                    cwd=lab.ROOT, check=True, capture_output=True)
-    subprocess.run(['cargo', 'build', '--release', '-p', 'horizon-client', '--bin', 'horizon-client'], cwd=lab.ROOT,
+    subprocess.run(['cargo', 'build', '--profile', 'fast', '-p', 'horizon-client', '--bin', 'horizon-client'], cwd=lab.ROOT,
                    check=True, capture_output=True)
-    binary = lab.cargo_target() / 'release' / ('horizon-client.exe' if os.name == 'nt' else 'horizon-client')
+    binary = lab.cargo_target() / 'fast' / ('horizon-client.exe' if os.name == 'nt' else 'horizon-client')
     vanilla_server = ['java', '-Xmx2g', '-Duser.timezone=UTC', '-cp', dependencies, 'net.minecraft.server.Main', 'nogui']
     horizon_server = [binary, '--resources', lab.LOCAL / 'horizon-client/26.3', '--dedicated', '--nogui']
     client = ['java', '-Xmx1g', '-cp', str(classes) + os.pathsep + dependencies, 'dev.horizonlab.parity.ServerPackClient']
diff --git a/tools/test_server_world_gen_parity.py b/tools/test_server_world_gen_parity.py
index f55e558097..14da72a6d9 100644
--- a/tools/test_server_world_gen_parity.py
+++ b/tools/test_server_world_gen_parity.py
@@ -130,11 +130,11 @@ def main():
     build.mkdir(parents=True, exist_ok=True)
     report = build / 'report.json'
     report.unlink(missing_ok=True)
-    subprocess.run(['cargo', 'build', '--release', '-p', 'horizon-client', '--bin', 'horizon-client'], cwd=lab.ROOT,
+    subprocess.run(['cargo', 'build', '--profile', 'fast', '-p', 'horizon-client', '--bin', 'horizon-client'], cwd=lab.ROOT,
                    check=True, capture_output=True)
     metadata = json.loads(subprocess.check_output(['cargo', 'metadata', '--no-deps', '--format-version', '1'],
                                                   cwd=lab.ROOT, text=True))
-    binary = Path(metadata['target_directory']) / 'release' / ('horizon-client.exe' if os.name == 'nt' else 'horizon-client')
+    binary = Path(metadata['target_directory']) / 'fast' / ('horizon-client.exe' if os.name == 'nt' else 'horizon-client')
     dependencies = os.pathsep.join(map(str, [jars['server'], *libraries]))
     vanilla_server = ['java', '-Xmx2g', '-Duser.timezone=UTC', '-cp', dependencies, 'net.minecraft.server.Main',
                       'nogui']
diff --git a/tools/test_spawn_rules_parity.py b/tools/test_spawn_rules_parity.py
index 7f9ac07ce0..01196b3552 100644
--- a/tools/test_spawn_rules_parity.py
+++ b/tools/test_spawn_rules_parity.py
@@ -155,9 +155,9 @@ def main():
          '-cp', str(jars['server']) + os.pathsep + deps, '-d', classes, oracle], 'compile-java')
     run(['java', '-Xmx2G', '-cp', os.pathsep.join([str(classes), str(jars['server']), deps]),
          'dev.horizonlab.parity.VanillaSpawnRulesOracle', inputs, build / 'server.txt'], 'server')
-    run(['cargo', 'build', '--release', '-p', 'horizon-client', '--example', 'client_probe'], 'compile-rust')
+    run(['cargo', 'build', '--profile', 'fast', '-p', 'horizon-client', '--example', 'client_probe'], 'compile-rust')
     metadata = json.loads(subprocess.check_output(['cargo', 'metadata', '--no-deps', '--format-version', '1'], cwd=lab.ROOT, text=True))
-    binary = Path(metadata['target_directory']) / 'release/examples/client_probe'
+    binary = Path(metadata['target_directory']) / 'fast/examples/client_probe'
     run([binary, 'spawn_rules_fixture', resources, inputs, build / 'rust.txt'], 'rust')
     vanilla = (build / 'server.txt').read_text().splitlines()
     errors = [l for l in vanilla if ' error ' in l]
diff --git a/tools/test_spawner_parity.py b/tools/test_spawner_parity.py
index 187e211b7c..34f6ec7268 100644
--- a/tools/test_spawner_parity.py
+++ b/tools/test_spawner_parity.py
@@ -249,9 +249,9 @@ def main():
          '-cp', str(jars['server']) + os.pathsep + deps, '-d', classes, oracle], 'compile-java')
     run(['java', '-Xmx3G', '-cp', os.pathsep.join([str(classes), str(jars['server']), deps]),
          'dev.horizonlab.parity.VanillaNaturalSpawnOracle', inputs, build / 'server.txt'], 'server')
-    run(['cargo', 'build', '--release', '-p', 'horizon-client', '--example', 'client_probe'], 'compile-rust')
+    run(['cargo', 'build', '--profile', 'fast', '-p', 'horizon-client', '--example', 'client_probe'], 'compile-rust')
     metadata = json.loads(subprocess.check_output(['cargo', 'metadata', '--no-deps', '--format-version', '1'], cwd=lab.ROOT, text=True))
-    binary = Path(metadata['target_directory']) / 'release/examples/client_probe'
+    binary = Path(metadata['target_directory']) / 'fast/examples/client_probe'
     run([binary, 'natural_spawn_fixture', resources, inputs, build / 'rust.txt'], 'rust')
     vanilla = (build / 'server.txt').read_text().splitlines()
     errors = [l for l in vanilla if ' error ' in l]
diff --git a/tools/test_subtitle_parity.py b/tools/test_subtitle_parity.py
index 6baf25570b..17c8565507 100644
--- a/tools/test_subtitle_parity.py
+++ b/tools/test_subtitle_parity.py
@@ -133,9 +133,9 @@ def main():
          *(PARITY / f'{n}.java' for n in ('ParityFont', 'VanillaSubtitleOracle'))], 'compile-java')
     run(['java', '-Xmx1G', '-cp', str(classes) + os.pathsep + dependencies, 'dev.horizonlab.parity.VanillaSubtitleOracle',
          inputs, build / 'vanilla.jsonl'], 'vanilla')
-    run(['cargo', 'build', '--release', '-p', 'horizon-client', '--example', 'client_probe'], 'compile-rust')
+    run(['cargo', 'build', '--profile', 'fast', '-p', 'horizon-client', '--example', 'client_probe'], 'compile-rust')
     metadata = json.loads(subprocess.check_output(['cargo', 'metadata', '--no-deps', '--format-version', '1'], cwd=lab.ROOT, text=True))
-    binary = Path(metadata['target_directory']) / 'release/examples' / ('client_probe.exe' if os.name=='nt' else 'client_probe')
+    binary = Path(metadata['target_directory']) / 'fast/examples' / ('client_probe.exe' if os.name=='nt' else 'client_probe')
     run([binary, 'subtitle_fixture',resources, inputs, build / 'rust.jsonl'], 'rust')
     vanilla = [json.loads(l) for l in (build / 'vanilla.jsonl').read_text(encoding='utf-8').splitlines()]
     rust = [json.loads(l) for l in (build / 'rust.jsonl').read_text(encoding='utf-8').splitlines()]
diff --git a/tools/test_team_rules_parity.py b/tools/test_team_rules_parity.py
index ac66a412bd..9d12075ec8 100644
--- a/tools/test_team_rules_parity.py
+++ b/tools/test_team_rules_parity.py
@@ -84,9 +84,9 @@ def main():
          PARITY / 'VanillaTeamRulesOracle.java'], 'compile-java')
     run(['java', '-Xmx1G', '-cp', str(classes) + os.pathsep + dependencies, 'dev.horizonlab.parity.VanillaTeamRulesOracle',
          inputs, build / 'vanilla.jsonl'], 'vanilla')
-    run(['cargo', 'build', '--release', '-p', 'horizon-client', '--example', 'client_probe'], 'compile-rust')
+    run(['cargo', 'build', '--profile', 'fast', '-p', 'horizon-client', '--example', 'client_probe'], 'compile-rust')
     metadata = json.loads(subprocess.check_output(['cargo', 'metadata', '--no-deps', '--format-version', '1'], cwd=lab.ROOT, text=True))
-    binary = Path(metadata['target_directory']) / 'release/examples' / ('client_probe.exe' if os.name=='nt' else 'client_probe')
+    binary = Path(metadata['target_directory']) / 'fast/examples' / ('client_probe.exe' if os.name=='nt' else 'client_probe')
     run([binary, 'team_rules_fixture',inputs, build / 'rust.jsonl'], 'rust')
     vanilla = [json.loads(l) for l in (build / 'vanilla.jsonl').read_text().splitlines()]
     rust = [json.loads(l) for l in (build / 'rust.jsonl').read_text().splitlines()]
diff --git a/tools/test_trading_parity.py b/tools/test_trading_parity.py
index 46e81f9282..9b5581f3b1 100644
--- a/tools/test_trading_parity.py
+++ b/tools/test_trading_parity.py
@@ -219,8 +219,8 @@ def main():
     if args.java_only:
         print(f'{len(vanilla)} oracle lines')
         return
-    run(['cargo', 'build', '--release', '-p', 'horizon-client', '--example', 'client_probe'], 'compile-rust')
-    binary = lab.cargo_target() / 'release/examples/client_probe'
+    run(['cargo', 'build', '--profile', 'fast', '-p', 'horizon-client', '--example', 'client_probe'], 'compile-rust')
+    binary = lab.cargo_target() / 'fast/examples/client_probe'
     run([binary, 'trading_fixture', resources, inputs, build / 'server.txt', build / 'rust.txt'], 'rust')
     rust = (build / 'rust.txt').read_text().splitlines()
     bad = [(a, b) for a, b in zip(vanilla, rust) if a != b]
diff --git a/tools/test_trial_spawner_parity.py b/tools/test_trial_spawner_parity.py
index 7b2412eaa4..43d26338a8 100644
--- a/tools/test_trial_spawner_parity.py
+++ b/tools/test_trial_spawner_parity.py
@@ -214,9 +214,9 @@ def main():
          '-cp', str(jars['server']) + os.pathsep + deps, '-d', classes, oracle], 'compile-java')
     run(['java', '-Xmx3G', '-cp', os.pathsep.join([str(classes), str(jars['server']), deps]),
          'dev.horizonlab.parity.VanillaNaturalSpawnOracle', inputs, build / 'server.txt'], 'server')
-    run(['cargo', 'build', '--release', '-p', 'horizon-client', '--example', 'client_probe'], 'compile-rust')
+    run(['cargo', 'build', '--profile', 'fast', '-p', 'horizon-client', '--example', 'client_probe'], 'compile-rust')
     metadata = json.loads(subprocess.check_output(['cargo', 'metadata', '--no-deps', '--format-version', '1'], cwd=lab.ROOT, text=True))
-    binary = Path(metadata['target_directory']) / 'release/examples/client_probe'
+    binary = Path(metadata['target_directory']) / 'fast/examples/client_probe'
     run([binary, 'natural_spawn_fixture', resources, inputs, build / 'rust.txt'], 'rust')
     vanilla = (build / 'server.txt').read_text().splitlines()
     errors = [l for l in vanilla if ' error ' in l]
diff --git a/tools/test_use_item_on_parity.py b/tools/test_use_item_on_parity.py
index eabdd04eb4..35e1c5515e 100644
--- a/tools/test_use_item_on_parity.py
+++ b/tools/test_use_item_on_parity.py
@@ -405,9 +405,9 @@ def main():
            '-cp', dependencies, '-d', str(classes), str(java_root / 'dev/horizonlab/parity/VanillaDispenserOracle.java')])
     d.run(['java', '-Xmx3G', '-cp', str(classes) + os.pathsep + dependencies, 'dev.horizonlab.parity.VanillaDispenserOracle',
            str(resources), str(work / 'cases.jsonl'), str(work / 'native.txt')])
-    d.run(['cargo', 'build', '-q', '--release', '-p', 'horizon-client', '--bin', 'horizon-client'], cwd=lab.ROOT,
+    d.run(['cargo', 'build', '-q', '--profile', 'fast', '-p', 'horizon-client', '--bin', 'horizon-client'], cwd=lab.ROOT,
           env={**os.environ, 'CARGO_BUILD_JOBS': os.environ.get('CARGO_BUILD_JOBS', '3')})
-    d.run([str(lab.cargo_target() / 'release/horizon-client'), '--resources', str(resources)], cwd=work,
+    d.run([str(lab.cargo_target() / 'fast/horizon-client'), '--resources', str(resources)], cwd=work,
           env=lab.game_env(HORIZON_DISPENSE_FIXTURE=f'{work / "cases.jsonl"},{work / "rust.txt"}'))
     ignore = tuple(prefix + ' ' for prefix in args.ignore.split(',') if prefix) + ('D ',)
     native = h.split_cases((work / 'native.txt').read_text(), ignore)
diff --git a/tools/test_user_cache_parity.py b/tools/test_user_cache_parity.py
index 621514cc8c..34a7af1f3d 100644
--- a/tools/test_user_cache_parity.py
+++ b/tools/test_user_cache_parity.py
@@ -205,11 +205,11 @@ def main():
     build.mkdir(parents=True, exist_ok=True)
     report = build / 'report.json'
     report.unlink(missing_ok=True)
-    subprocess.run(['cargo', 'build', '--release', '-p', 'horizon-client', '--bin', 'horizon-client'], cwd=lab.ROOT,
+    subprocess.run(['cargo', 'build', '--profile', 'fast', '-p', 'horizon-client', '--bin', 'horizon-client'], cwd=lab.ROOT,
                    check=True, capture_output=True)
     metadata = json.loads(subprocess.check_output(['cargo', 'metadata', '--no-deps', '--format-version', '1'],
                                                   cwd=lab.ROOT, text=True))
-    binary = Path(metadata['target_directory']) / 'release' / ('horizon-client.exe' if os.name == 'nt' else 'horizon-client')
+    binary = Path(metadata['target_directory']) / 'fast' / ('horizon-client.exe' if os.name == 'nt' else 'horizon-client')
     services = Services()
     discovery = services.url + '/minecraft/client'
     dependencies = os.pathsep.join(map(str, [jars['server'], *libraries]))
diff --git a/tools/test_vault_parity.py b/tools/test_vault_parity.py
index 5741320d35..00e6422f51 100644
--- a/tools/test_vault_parity.py
+++ b/tools/test_vault_parity.py
@@ -190,9 +190,9 @@ def main():
          '-cp', str(jars['server']) + os.pathsep + deps, '-d', classes, oracle], 'compile-java')
     run(['java', '-Xmx3G', '-cp', os.pathsep.join([str(classes), str(jars['server']), deps]),
          'dev.horizonlab.parity.VanillaNaturalSpawnOracle', inputs, build / 'server.txt'], 'server')
-    run(['cargo', 'build', '--release', '-p', 'horizon-client', '--example', 'client_probe'], 'compile-rust')
+    run(['cargo', 'build', '--profile', 'fast', '-p', 'horizon-client', '--example', 'client_probe'], 'compile-rust')
     metadata = json.loads(subprocess.check_output(['cargo', 'metadata', '--no-deps', '--format-version', '1'], cwd=lab.ROOT, text=True))
-    binary = Path(metadata['target_directory']) / 'release/examples/client_probe'
+    binary = Path(metadata['target_directory']) / 'fast/examples/client_probe'
     run([binary, 'natural_spawn_fixture', resources, inputs, build / 'rust.txt'], 'rust')
     vanilla = (build / 'server.txt').read_text().splitlines()
     errors = [l for l in vanilla if ' error ' in l]
diff --git a/tools/test_world_spawn_parity.py b/tools/test_world_spawn_parity.py
index 00c390005a..33bdd4c65c 100644
--- a/tools/test_world_spawn_parity.py
+++ b/tools/test_world_spawn_parity.py
@@ -69,10 +69,10 @@ def seeds(count):
     return SEEDS + [rng.randrange(-2**63, 2**63) for _ in range(count)]
 
 
-def target_dir():
+def target_dir(profile='release'):
     metadata = json.loads(subprocess.check_output(['cargo', 'metadata', '--no-deps', '--format-version', '1'],
                                                   cwd=lab.ROOT, text=True))
-    return Path(metadata['target_directory']) / 'release'
+    return Path(metadata['target_directory']) / profile
 
 
 def origins(build, classes, dependencies, all_seeds):
@@ -134,9 +134,9 @@ def main():
     if args.origins_only:
         sys.exit(1 if origin_diffs else 0)
 
-    oh.run_logged(['cargo', 'build', '--release', '-p', 'horizon-client', '--bin', 'horizon-client'], build,
+    oh.run_logged(['cargo', 'build', '--profile', 'fast', '-p', 'horizon-client', '--bin', 'horizon-client'], build,
                   'compile-rust', timeout=3600)
-    binary = target_dir() / ('horizon-client.exe' if os.name == 'nt' else 'horizon-client')
+    binary = target_dir('fast') / ('horizon-client.exe' if os.name == 'nt' else 'horizon-client')
     # One worker thread: the chunks decorated in a fixed order (see above).
     vanilla_server = ['java', '-Xmx2g', '-Dmax.bg.threads=1', '-cp', dependencies, 'net.minecraft.server.Main', 'nogui']
     horizon_server = [binary, '--resources', RESOURCES, '--dedicated', '--nogui']