feat(pricing): add Fable 5.1 and Mythos 5.1

internal/cost/cost_test.go

@@ -33,6 +33,8 @@ func TestLookupPrefixAndProviderIDs(t *testing.T) {
 		"claude-3-5-haiku-20241022":                    "claude-3-5-haiku",
 		"CLAUDE-HAIKU-4-5":                             "claude-haiku-4-5",
 		"anthropic.claude-opus-4-1-20250805-v1:0":      "claude-opus-4-1",
+		"claude-fable-5-1":                             "claude-fable-5-1",
+		"claude-fable-5":                               "claude-fable-5",
 	}
 	for in, want := range cases {
 		row, ok := tb.Lookup(in)
@@ -226,3 +228,28 @@ func TestEveryModelHasExactlyOneCurrentPrice(t *testing.T) {
 		}
 	}
 }
+
+func TestFable51CacheReadsAtItsOwnRate(t *testing.T) {
+	tb, _ := Embedded()
+
+	// Fable 5.1 reads cache at 0.025x input, not the 0.1x every other row
+	// follows, so the $0.25 looks like a typo of Fable 5's $1.00 and sits one
+	// character away from a row that would charge four times as much.
+	for _, tc := range []struct {
+		model string
+		want  float64
+	}{
+		{"claude-fable-5-1", 0.25},
+		{"claude-mythos-5-1", 0.25},
+		{"claude-fable-5", 1.0},
+	} {
+		got, ok := tb.Price(tc.model, event.TokenDelta{CacheRead: 1_000_000})
+		if !ok {
+			t.Errorf("%s has no price", tc.model)
+			continue
+		}
+		if got != tc.want {
+			t.Errorf("%s: 1M cache-read tokens cost $%.2f, want $%.2f", tc.model, got, tc.want)
+		}
+	}
+}

pricing/pricing.json

@@ -1,12 +1,12 @@
 {
-  "version": "2026-09-01.1",
+  "version": "2026-09-02.1",
   "source": "https://platform.claude.com/docs/en/about-claude/pricing",
   "fetched_at": "2026-08-18",
   "currency": "USD",
   "unit": "per_million_tokens",
   "notes": [
     "First-party Anthropic API prices. Amazon Bedrock and Google Vertex have separate partner pricing (regional endpoints +10%) and are not covered by this table (OQ-02).",
-    "cache_write_5m = 1.25x input, cache_write_1h = 2x input, cache_read = 0.1x input \u2014 per Anthropic's published multipliers.",
+    "cache_write_5m = 1.25x input, cache_write_1h = 2x input, cache_read = 0.1x input \u2014 per Anthropic's published multipliers. Claude Fable 5.1 and Claude Mythos 5.1 are the exception and read 0.025x ($0.25 per 1M), so those two rows deliberately break the 0.1x rule; both were read from the pricing page on 2026-09-02.",
     "Model ids are matched by prefix against the `model` field observed in transcripts (e.g. claude-opus-5, claude-sonnet-4-5-20250929). Longest prefix wins.",
     "context_window is the model's maximum input context in tokens as published; used for the 'context fill %' badge (OQ-07).",
     "Non-Anthropic rows are the providers' own published list prices, fetched 2026-08-27: DeepSeek V4 Pro $0.435/$0.87 per 1M (its 75% cut, made permanent); MiniMax M3 $0.30/$1.20 per 1M standard tier with $0.06 cache read (its permanent 50% off). They are priced so a total that includes non-Anthropic usage is a total; Caprock still does not charge for any of it and cannot see a bill.",
@@ -17,6 +17,26 @@
     "gemini-3.1-pro-preview and gemini-2.5-pro are tiered by prompt size; the rate here is the =<200k tier. Prompts over 200k tokens bill at roughly double ($4.00/$18.00 and $2.50/$15.00 respectively) and are therefore under-reported by this table."
   ],
   "models": [
+    {
+      "id": "claude-fable-5-1",
+      "display": "Claude Fable 5.1",
+      "input": 10.0,
+      "cache_write_5m": 12.5,
+      "cache_write_1h": 20.0,
+      "cache_read": 0.25,
+      "output": 50.0,
+      "context_window": 1000000
+    },
+    {
+      "id": "claude-mythos-5-1",
+      "display": "Claude Mythos 5.1",
+      "input": 10.0,
+      "cache_write_5m": 12.5,
+      "cache_write_1h": 20.0,
+      "cache_read": 0.25,
+      "output": 50.0,
+      "context_window": 1000000
+    },
     {
       "id": "claude-fable-5",
       "display": "Claude Fable 5",