feat: add Claude Opus 5.5 as a benchmark pricing model

cmd/cc-session/benchmark.go

@@ -30,7 +30,7 @@ func runBenchmark(args []string, out io.Writer, errOut io.Writer, store parser.S
 	days := fs.Int("days", 30, "how far back to scan")
 	minKB := fs.Int("min-kb", 100, "minimum JSONL file size in KB")
 	maxN := fs.Int("n", 10, "max sessions to include")
-	model := fs.String("model", "opus", "model: opus, opus-4-6, opus-4-7, opus-4-8, sonnet, or fable (fable-5-1)")
+	model := fs.String("model", "opus", "model: opus, opus-4-6, opus-4-7, opus-4-8, opus-5-5, sonnet, or fable (fable-5-1)")
 	overhead := fs.Int("overhead", 0, "session overhead tokens (system+tools+CLAUDE.md); measure with a 1-turn session")
 	isNoAPI := fs.Bool("no-api", false, "skip API calls; estimate filtered-text tokens with chars/2 (offline fallback)")
 	if err := fs.Parse(reorderArgs(args)); err != nil {

docs/benchmark.md

@@ -36,7 +36,7 @@ All other parameters are derived automatically from your real session data.
 | `--days` | 30 | How far back to scan for sessions |
 | `--min-kb` | 100 | Minimum JSONL file size in KB |
 | `--n` | 10 | Max successful session results to report |
-| `--model` | opus | Pricing and token-counting model: `opus`, `opus-4-6`, `opus-4-7`, `opus-4-8`, `sonnet`, or `fable` (`fable-5-1`) |
+| `--model` | opus | Pricing and token-counting model: `opus`, `opus-4-6`, `opus-4-7`, `opus-4-8`, `opus-5-5`, `sonnet`, or `fable` (`fable-5-1`) |
 
 ### Example output
 
@@ -62,12 +62,12 @@ Median break-even: turn 1 | 10-turn saving: 69% | 100-turn saving: 48%
 
 From [Anthropic prompt caching docs](https://platform.claude.com/docs/en/build-with-claude/prompt-caching):
 
-| Bucket | API field | Rate (Opus) |
-|--------|-----------|:-----------:|
-| Cache read | `cache_read_input_tokens` | $0.50/M (0.1× base) |
-| Cache write | `cache_creation_input_tokens` | $6.25/M (1.25× base) |
-| Uncached input | `input_tokens` | $5.00/M (1× base) |
-| Output | `output_tokens` | $25/M (excluded — same for both scenarios) |
+| Bucket | API field | Rate (Opus 4.x) | Rate (Opus 5.5) |
+|--------|-----------|:-----------:|:-----------:|
+| Cache read | `cache_read_input_tokens` | $0.50/M (0.1× base) | $0.20/M (0.05× base) |
+| Cache write | `cache_creation_input_tokens` | $6.25/M (1.25× base) | $5.00/M (1.25× base) |
+| Uncached input | `input_tokens` | $5.00/M (1× base) | $4.00/M (1× base) |
+| Output | `output_tokens` | $25/M (excluded — same for both scenarios) | $20/M (excluded) |
 
 ### Per-API-call billing
 
@@ -162,16 +162,18 @@ the historical one-shot `NewCtx × CacheWrite` behavior.
 
 `X` comes from transcript API usage and `C` comes from the Anthropic token
 counting API. The `--model` flag controls both pricing and the tokenizer used by
-the token counting API. `opus` is an alias for `opus-4-8`; explicit Opus versions
-map to `claude-opus-4-6`, `claude-opus-4-7`, or `claude-opus-4-8`; `sonnet` maps
-to `claude-sonnet-4-6`; `fable` and `fable-5-1` both map to `claude-fable-5-1`.
-Opus 4.6, 4.7, and 4.8 use the same Opus pricing rates.
+the token counting API. `opus` is an alias for `opus-4-8`; explicit Opus 4.x
+versions map to `claude-opus-4-6`, `claude-opus-4-7`, or `claude-opus-4-8`;
+`opus-5-5` maps to `claude-opus-5-5`; `sonnet` maps to `claude-sonnet-4-6`;
+`fable` and `fable-5-1` both map to `claude-fable-5-1`.
+Opus 4.6, 4.7, and 4.8 use the same Opus pricing rates; Opus 5.5 has its own,
+lower rates (see the pricing table above).
 Fallback constants are used only for behavior that cannot be read directly from
 transcript usage, such as sparse tool I/O data.
 
-Claude Fable 5.1's cache read is 2.5% of base input, not the 10% every other
-model here uses, so its cost-savings numbers are not directly comparable to the
-Opus/Sonnet rows.
+Cache read as a percentage of base input differs by model: Opus 4.x and Sonnet
+use 10%, Opus 5.5 uses 5%, and Claude Fable 5.1 uses 2.5%. Cost-savings numbers
+are only directly comparable across rows using the same ratio.
 
 ### Simplifications
 

internal/benchmark/model.go

@@ -12,16 +12,24 @@ type Pricing struct {
 var PricingOpus = Pricing{CachedRead: 0.50, CacheWrite: 6.25, BaseInput: 5.00}
 var PricingSonnet = Pricing{CachedRead: 0.30, CacheWrite: 3.75, BaseInput: 3.00}
 
-// PricingFable is Claude Fable 5.1's pricing. Unlike every other tier here, its
-// cache read is 2.5% of base input rather than the usual 10% (source: Anthropic
-// pricing docs, "a cache hit costs 2.5% of the standard input price"), so its
-// cost-savings numbers are not directly comparable to the Opus/Sonnet rows.
+// PricingOpus55 is Claude Opus 5.5's pricing. Its cache read is 5% of base
+// input rather than the 10% Opus 4.x/Sonnet use (source: Anthropic pricing
+// docs, "a cache hit costs 5% of the standard input price"), so its
+// cost-savings numbers are not directly comparable to the Opus 4.x/Sonnet rows.
+var PricingOpus55 = Pricing{CachedRead: 0.20, CacheWrite: 5.00, BaseInput: 4.00}
+
+// PricingFable is Claude Fable 5.1's pricing. Its cache read is 2.5% of base
+// input — lower than the 10% Opus 4.x/Sonnet use and the 5% Opus 5.5 uses
+// (source: Anthropic pricing docs, "a cache hit costs 2.5% of the standard
+// input price"), so its cost-savings numbers are not directly comparable to
+// the other rows.
 var PricingFable = Pricing{CachedRead: 0.25, CacheWrite: 12.50, BaseInput: 10.00}
 
 const (
 	TokenCountModelOpus46 = "claude-opus-4-6"
 	TokenCountModelOpus47 = "claude-opus-4-7"
 	TokenCountModelOpus48 = "claude-opus-4-8"
+	TokenCountModelOpus55 = "claude-opus-5-5"
 	TokenCountModelSonnet = "claude-sonnet-4-6"
 	TokenCountModelFable  = "claude-fable-5-1"
 )
@@ -43,10 +51,12 @@ func ResolveModel(model string) (ModelConfig, error) {
 		return ModelConfig{Pricing: PricingOpus, TokenCountModel: TokenCountModelOpus47}, nil
 	case "opus-4-6":
 		return ModelConfig{Pricing: PricingOpus, TokenCountModel: TokenCountModelOpus46}, nil
+	case "opus-5-5":
+		return ModelConfig{Pricing: PricingOpus55, TokenCountModel: TokenCountModelOpus55}, nil
 	case "fable", "fable-5-1":
 		return ModelConfig{Pricing: PricingFable, TokenCountModel: TokenCountModelFable}, nil
 	default:
-		return ModelConfig{}, fmt.Errorf("unknown model %q: must be opus, opus-4-6, opus-4-7, opus-4-8, sonnet, fable, or fable-5-1", model)
+		return ModelConfig{}, fmt.Errorf("unknown model %q: must be opus, opus-4-6, opus-4-7, opus-4-8, opus-5-5, sonnet, fable, or fable-5-1", model)
 	}
 }
 

internal/benchmark/model_test.go

@@ -42,6 +42,12 @@ func Test_ResolveModel_GivenKnownAlias_ThenReturnsExpectedConfig(t *testing.T) {
 			wantPricing:    PricingOpus,
 			wantTokenCount: TokenCountModelOpus46,
 		},
+		{
+			name:           "opus-5-5",
+			alias:          "opus-5-5",
+			wantPricing:    PricingOpus55,
+			wantTokenCount: TokenCountModelOpus55,
+		},
 		{
 			name:           "fable",
 			alias:          "fable",
@@ -73,7 +79,7 @@ func Test_ResolveModel_GivenKnownAlias_ThenReturnsExpectedConfig(t *testing.T) {
 }
 
 // Regression guard: PricingFable's cache read must stay at 2.5% of base input
-// ($0.25/MTok), not the 10% ratio every other tier in this file uses.
+// ($0.25/MTok), not the 10% ratio Opus 4.x/Sonnet use.
 func Test_PricingFable_ThenCacheReadIsTwoPointFivePercentOfBaseInput(t *testing.T) {
 	want := PricingFable.BaseInput * 0.025
 	if PricingFable.CachedRead != want {
@@ -82,6 +88,16 @@ func Test_PricingFable_ThenCacheReadIsTwoPointFivePercentOfBaseInput(t *testing.
 	}
 }
 
+// Regression guard: PricingOpus55's cache read must stay at 5% of base input
+// ($0.20/MTok), not the 10% ratio Opus 4.x/Sonnet use.
+func Test_PricingOpus55_ThenCacheReadIsFivePercentOfBaseInput(t *testing.T) {
+	want := PricingOpus55.BaseInput * 0.05
+	if PricingOpus55.CachedRead != want {
+		t.Errorf("PricingOpus55.CachedRead = %v, want %v (5%% of BaseInput %v)",
+			PricingOpus55.CachedRead, want, PricingOpus55.BaseInput)
+	}
+}
+
 func Test_ResolveModel_GivenUnknownAlias_ThenErrorListsFableAliases(t *testing.T) {
 	_, err := ResolveModel("nonsense")
 	if err == nil {
@@ -91,3 +107,13 @@ func Test_ResolveModel_GivenUnknownAlias_ThenErrorListsFableAliases(t *testing.T
 		t.Errorf("error = %v, want it to list the fable aliases", err)
 	}
 }
+
+func Test_ResolveModel_GivenUnknownAlias_ThenErrorListsOpus55Alias(t *testing.T) {
+	_, err := ResolveModel("nonsense")
+	if err == nil {
+		t.Fatal("ResolveModel(\"nonsense\") returned nil error, want unknown model error")
+	}
+	if !strings.Contains(err.Error(), "opus-5-5") {
+		t.Errorf("error = %v, want it to list the opus-5-5 alias", err)
+	}
+}