feat(pricing): Google's Gemini rates, with a dated generation for the announced step

cmd/reasonix-studio-host/main.go

@@ -48,6 +48,7 @@ import (
 	// Kinds register from init, so a binary builds only what it links. Without
 	// these every Anthropic model answers "unknown kind" at switch time.
 	_ "reasonix/internal/model/anthropic"
+	_ "reasonix/internal/model/gemini"
 	_ "reasonix/internal/model/openai"
 	_ "reasonix/internal/model/responses"
 )

cmd/reasonix/main.go

@@ -12,6 +12,7 @@ import (
 
 	// Blank imports wire compile-time built-ins into their registries.
 	_ "reasonix/internal/model/anthropic"
+	_ "reasonix/internal/model/gemini"
 	_ "reasonix/internal/model/openai"
 	_ "reasonix/internal/model/responses"
 	_ "reasonix/internal/tools/builtin"

internal/contract/config/protocol.go

@@ -46,6 +46,9 @@ var protocols = []Protocol{
 	{Kind: "openai", Answers: AnswersChat, Discovery: "openai", ReasoningParams: true, EffortField: "reasoning_effort", EffortUnder: []string{ReasoningProtocolOpenAI}, EffortUnresolved: true},
 	{Kind: "responses", Answers: AnswersChat, Discovery: "openai", ServerWebSearch: true, ReasoningParams: true, StatefulContinuation: true, EffortField: "reasoning.effort"},
 	{Kind: "anthropic", Answers: AnswersChat, Discovery: "anthropic", ServerWebSearch: true, EffortField: "output_config.effort", EffortUnder: []string{ReasoningProtocolAnthropic}},
+	// No Discovery: Google's model listing shape is not read for this wire yet,
+	// so a Gemini model id is declared rather than probed for.
+	{Kind: "gemini", Answers: AnswersChat, EffortField: "generation_config.thinking_level"},
 	// No Discovery: the decision API has no model listing, so the model id is
 	// declared rather than probed for.
 	{Kind: "typesafe", Answers: AnswersDecision},

internal/contract/config/protocol_effort_field_test.go

@@ -10,6 +10,7 @@ func TestProtocolsDeclareWhereEffortLands(t *testing.T) {
 		"openai":    "reasoning_effort",
 		"responses": "reasoning.effort",
 		"anthropic": "output_config.effort",
+		"gemini":    "generation_config.thinking_level",
 		"typesafe":  "",
 	}
 	seen := 0

internal/contract/config/protocol_test.go

@@ -6,6 +6,7 @@ import (
 
 	"reasonix/internal/contract/provider"
 	_ "reasonix/internal/model/anthropic"
+	_ "reasonix/internal/model/gemini"
 	_ "reasonix/internal/model/openai"
 	_ "reasonix/internal/model/responses"
 )

internal/contract/pricing/catalog.go

@@ -11,7 +11,7 @@ import (
 
 // CatalogEntry is one official list price for a model in a billing currency.
 type CatalogEntry struct {
-	Provider      string // deepseek | longcat | mimo
+	Provider      string // deepseek | longcat | mimo | google
 	Model         string
 	Currency      string // ISO billing currency for this row
 	CacheHit      float64
@@ -76,6 +76,9 @@ const deepseekCheckedOn = "2026-09-13"
 // mimoCheckedOn is when the V2.6 rows were read off the vendor's own docs.
 const mimoCheckedOn = "2026-10-06"
 
+// googleCheckedOn is when the Gemini rows were read off Google's pricing page.
+const googleCheckedOn = "2026-10-17"
+
 // CatalogSourceURLs document public pricing pages.
 const (
 	DocDeepSeekPricing    = "https://api-docs.deepseek.com/quick_start/pricing"
@@ -84,6 +87,7 @@ const (
 	DocLongCatPricingCNY  = "https://longcat.chat/platform/docs/zh/pricing/long-cat-2.0"
 	DocMiMoPAYG           = "https://mimo.mi.com/docs/price/pay-as-you-go"
 	DocMiMoTokenPlan      = "https://platform.xiaomimimo.com/token-plan"
+	DocGeminiPricing      = "https://ai.google.dev/gemini-api/docs/pricing"
 )
 
 // officialEndpointHosts maps a vendor's own API hostnames to the catalog
@@ -91,12 +95,13 @@ const (
 // or proxy bills on its own terms even when it serves the same model, and an
 // entry merely named after a vendor is not evidence of the vendor's endpoint.
 var officialEndpointHosts = map[string]string{
-	"api.deepseek.com":              "deepseek",
-	"api.longcat.chat":              "longcat",
-	"api.xiaomimimo.com":            "mimo",
-	"token-plan-cn.xiaomimimo.com":  "mimo",
-	"token-plan-sgp.xiaomimimo.com": "mimo",
-	"token-plan-ams.xiaomimimo.com": "mimo",
+	"api.deepseek.com":                  "deepseek",
+	"api.longcat.chat":                  "longcat",
+	"api.xiaomimimo.com":                "mimo",
+	"generativelanguage.googleapis.com": "google",
+	"token-plan-cn.xiaomimimo.com":      "mimo",
+	"token-plan-sgp.xiaomimimo.com":     "mimo",
+	"token-plan-ams.xiaomimimo.com":     "mimo",
 }
 
 // OfficialProviderForEndpoint returns the catalog provider whose official

internal/contract/pricing/google_rates_test.go

@@ -0,0 +1,68 @@
+package pricing
+
+import "testing"
+
+// https://ai.google.dev/gemini-api/docs/pricing (read 2026-10-17): per 1M tokens,
+// paid tier. gemini-3.8-flash is 0.75 in / 3.75 out / 0.075 cached through
+// 2026-12-31 and 1.50 / 7.50 / 0.15 from 2027-01-01.
+func TestAGeminiRateStepIsDatedNotEdited(t *testing.T) {
+	was := today
+	defer func() { today = was }()
+	for _, tc := range []struct {
+		day                  string
+		cache, input, output float64
+	}{
+		{"2026-10-17", 0.075, 0.75, 3.75},
+		{"2026-12-31", 0.075, 0.75, 3.75},
+		{"2027-01-01", 0.15, 1.50, 7.50},
+		{"2028-03-01", 0.15, 1.50, 7.50},
+	} {
+		today = func() string { return tc.day }
+		got := CurrentRate("google", "gemini-3.8-flash", "USD")
+		if got == nil || got.CacheHit != tc.cache || got.Input != tc.input || got.Output != tc.output {
+			t.Errorf("%s: rate = %+v, want %v/%v/%v", tc.day, got, tc.cache, tc.input, tc.output)
+		}
+	}
+}
+
+func TestTheRateInForceIsNotListedAsSuperseded(t *testing.T) {
+	was := today
+	defer func() { today = was }()
+	today = func() string { return "2026-10-17" }
+	if sup := SupersededRates("google", "gemini-3.8-flash", "USD"); len(sup) != 0 {
+		t.Fatalf("before the step nothing is superseded, got %+v", sup)
+	}
+	today = func() string { return "2027-02-01" }
+	sup := SupersededRates("google", "gemini-3.8-flash", "USD")
+	if len(sup) != 1 || sup[0].Input != 0.75 {
+		t.Fatalf("after the step the intro rate is superseded, got %+v", sup)
+	}
+	if !IsOfficialCard("google", "gemini-3.8-flash", RateCard{CacheHit: 0.075, Input: 0.75, Output: 3.75, Currency: "USD"}) {
+		t.Fatal("a stored intro card must still read as ours after the step")
+	}
+}
+
+func TestGoogleModelsAreBilledAtGoogleOnlyOnGoogleHosts(t *testing.T) {
+	if OfficialProviderForEndpoint("https://generativelanguage.googleapis.com/v1beta") != "google" {
+		t.Fatal("Google's own host does not read as Google")
+	}
+	if OfficialProviderForEndpoint("https://relay.example.com/v1beta") != "" {
+		t.Fatal("a relay was billed at Google's list price")
+	}
+}
+
+func TestEveryGoogleRowNamesItsSource(t *testing.T) {
+	n := 0
+	for _, e := range OfficialCatalog() {
+		if e.Provider != "google" {
+			continue
+		}
+		n++
+		if e.DocURL != DocGeminiPricing || e.CheckedOn != googleCheckedOn || e.Input <= 0 || e.Output <= e.Input {
+			t.Errorf("row %+v", e)
+		}
+	}
+	if n != 4 {
+		t.Fatalf("%d Google rows, want 4 (gemini-4-argon shows no price)", n)
+	}
+}

internal/contract/pricing/rates.go

@@ -5,6 +5,7 @@ package pricing
 import (
 	"slices"
 	"strings"
+	"time"
 )
 
 // rateGeneration is one published pair. Peak is nil for a generation the vendor
@@ -12,6 +13,26 @@ import (
 type rateGeneration struct {
 	Base RateCard
 	Peak *RateCard
+	// From is the first day (YYYY-MM-DD, UTC) the vendor bills this generation.
+	// Empty means it applies from the moment it was shipped. A vendor that
+	// announces a price change ahead of time gets the later generation appended
+	// now, with its date, rather than edited in when the day comes.
+	From string
+}
+
+// today is the day a dated generation is read against; a test replaces it.
+var today = func() string { return time.Now().UTC().Format("2006-01-02") }
+
+// currentIndex is the generation in force today: the last one whose date has
+// come. Rows with no dated generation answer with their last, as before.
+func (r officialRateRow) currentIndex() int {
+	day := today()
+	for i := len(r.Rates) - 1; i > 0; i-- {
+		if r.Rates[i].From == "" || r.Rates[i].From <= day {
+			return i
+		}
+	}
+	return 0
 }
 
 // officialRateRow is one vendor's model, in one currency, under one billing
@@ -89,6 +110,38 @@ var officialRates = []officialRateRow{
 		Rates: []rateGeneration{{Base: RateCard{CacheHit: 0.006, Input: 0.30, Output: 1.20, Currency: "USD"}}},
 	},
 
+	// Google bills one rate card per model; gemini-3.8-flash and gemini-3.6-flash
+	// double on 2027-01-01 per the page, which is why their second generation is
+	// dated. gemini-3.1-pro-preview bills more above 200k prompt tokens (cached
+	// 0.40, input 4.00, output 18.00), which one card cannot say, so the card is
+	// the rate up to 200k and Notes says so. gemini-4-argon shows no price.
+	{
+		Provider: "google", Model: "gemini-3.8-flash", Currency: "USD",
+		BillingMode: BillingModePAYG, DocURL: DocGeminiPricing, CheckedOn: googleCheckedOn,
+		Rates: []rateGeneration{
+			{Base: RateCard{CacheHit: 0.075, Input: 0.75, Output: 3.75, Currency: "USD"}},
+			{From: "2027-01-01", Base: RateCard{CacheHit: 0.15, Input: 1.50, Output: 7.50, Currency: "USD"}},
+		},
+	},
+	{
+		Provider: "google", Model: "gemini-3.6-flash", Currency: "USD",
+		BillingMode: BillingModePAYG, DocURL: DocGeminiPricing, CheckedOn: googleCheckedOn,
+		Rates: []rateGeneration{
+			{Base: RateCard{CacheHit: 0.075, Input: 0.75, Output: 3.75, Currency: "USD"}},
+			{From: "2027-01-01", Base: RateCard{CacheHit: 0.15, Input: 1.50, Output: 7.50, Currency: "USD"}},
+		},
+	},
+	{
+		Provider: "google", Model: "gemini-3.5-flash-lite", Currency: "USD",
+		BillingMode: BillingModePAYG, DocURL: DocGeminiPricing, CheckedOn: googleCheckedOn,
+		Rates: []rateGeneration{{Base: RateCard{CacheHit: 0.03, Input: 0.30, Output: 2.50, Currency: "USD"}}},
+	},
+	{
+		Provider: "google", Model: "gemini-3.1-pro-preview", Currency: "USD",
+		BillingMode: BillingModePAYG, DocURL: DocGeminiPricing, Notes: "up_to_200k_prompt_tokens", CheckedOn: googleCheckedOn,
+		Rates: []rateGeneration{{Base: RateCard{CacheHit: 0.20, Input: 2.00, Output: 12.00, Currency: "USD"}}},
+	},
+
 	// MiMo domestic PAYG; Token Plan bills the same rates as subscription_equivalent.
 	{
 		Provider: "mimo", Model: "mimo-v2.5-pro", Currency: "CNY",
@@ -221,7 +274,7 @@ func CurrentRate(provider, model, currency string) *RateCard {
 			continue
 		}
 		if len(row.Rates) > 0 {
-			rate := row.Rates[len(row.Rates)-1].Base
+			rate := row.Rates[row.currentIndex()].Base
 			return &rate
 		}
 	}
@@ -259,7 +312,7 @@ func SupersededRates(provider, model, currency string) []RateCard {
 		if row.BillingMode == BillingModeSubscriptionEquivalent || len(row.Rates) < 2 {
 			continue
 		}
-		for _, generation := range row.Rates[:len(row.Rates)-1] {
+		for _, generation := range row.Rates[:row.currentIndex()] {
 			out = append(out, generation.Base)
 		}
 	}
@@ -274,7 +327,7 @@ func officialCatalogRows() []CatalogEntry {
 		if len(row.Rates) == 0 {
 			continue
 		}
-		current := row.Rates[len(row.Rates)-1]
+		current := row.Rates[row.currentIndex()]
 		rows = append(rows, row.entry(row.Model, current))
 		if row.Provider != "deepseek" || row.Model != "deepseek-flash" {
 			continue

tools/pricecheck/sources.go

@@ -52,6 +52,12 @@ func sources() []source {
 			URL:    pricing.DocLongCatPricingCNY,
 			Read:   readLongCat,
 		},
+		{
+			Provider: "google", Currency: "USD",
+			Models: []string{"gemini-3.8-flash", "gemini-3.6-flash", "gemini-3.5-flash-lite", "gemini-3.1-pro-preview"},
+			URL:    pricing.DocGeminiPricing,
+			Unread: "no reader yet: the page lists several tiers and a dated step per model, so a person re-reads it and moves CheckedOn",
+		},
 		{
 			Provider: "mimo", Currency: "CNY",
 			Models: []string{"mimo-v2.6-pro", "mimo-v2.6-flash", "mimo-v2.6-pro-ultraspeed", "mimo-v2.5-pro", "mimo-v2.5", "mimo-v2-flash"},