[BOT ISSUE] Anthropic: add missing claude-mythos-5 and claude-mythos-preview models

[github-actions]

Summary

Two Anthropic models from the Project Glasswing program are documented on the official Anthropic models page with API IDs but are absent from packages/proxy/schema/model_list.json. The closely related claude-fable-5 (same pricing tier) is already in the catalog at line ~7956.

A prior issue (#814) was filed and closed for claude-mythos-5, but the model was never added to the catalog — grep for "mythos" in model_list.json returns zero matches.

Missing Models

Model ID	Display Name	Input $/MTok	Output $/MTok	Availability
claude-mythos-5	Claude Mythos 5	$10	$50	Limited (Project Glasswing)
claude-mythos-preview	Claude Mythos Preview	—	—	Limited (Project Glasswing)

claude-mythos-5 has explicit pricing on the Anthropic pricing page (identical to claude-fable-5). claude-mythos-preview is listed on the models page with an API model ID but does not have a separate pricing table entry.

Context

• Both models launched June 9, 2026 per Anthropic's models page
• Claude Mythos 5 "shares Claude Fable 5's specs and pricing" per the models page
• Both are offered in limited availability to approved customers through Project Glasswing
• The catalog already has claude-fable-5 with matching specs and pricing ($10/$50)
• Prior issue [BOT ISSUE] Anthropic: add missing claude-mythos-5 model #814 was closed on 2026-06-18 with PR chore: update model catalog from bot issues #822 referenced, but claude-mythos-5 is not in the current catalog

Suggested Catalog Entry

"claude-mythos-5": {
  "format": "anthropic",
  "flavor": "chat",
  "multimodal": true,
  "input_cost_per_mil_tokens": 10,
  "output_cost_per_mil_tokens": 50,
  "input_cache_read_cost_per_mil_tokens": 1,
  "input_cache_write_5m_cost_per_mil_tokens": 12.5,
  "input_cache_write_1h_cost_per_mil_tokens": 20,
  "displayName": "Claude Mythos 5",
  "reasoning": true,
  "reasoning_budget": true,
  "max_input_tokens": 1000000,
  "max_output_tokens": 128000,
  "available_providers": [
    "anthropic"
  ]
}

claude-mythos-preview entry should mirror the above but without pricing fields (no official pricing published for this specific model ID).

Verification Checklist

Check	Status	Detail
Cross-source	✅	claude-mythos-5 confirmed on Models overview (API ID in comparison section) AND Pricing page ($10/$50 per MTok)
Already fixed	✅	grep for mythos in model_list.json returns zero matches on current main (commit 7941217)
ID format	✅	Follows claude-{name}-{version} convention used by all Anthropic models
Duplicate check	✅	No existing open issue covers these models. Prior issue #814 is closed but model was never added

Verification Notes

Field	Source	Notes
Model ID claude-mythos-5	Anthropic Models page	Listed under "Claude Fable 5 and Claude Mythos 5" section
Model ID claude-mythos-preview	Anthropic Models page	"joins the invitation-only Claude Mythos Preview (claude-mythos-preview)"
input_cost_per_mil_tokens: 10	Anthropic Pricing page	Row: "Claude Mythos 5 (limited availability)"
output_cost_per_mil_tokens: 50	Anthropic Pricing page	Same row
Cache pricing (1 / 12.5 / 20)	Anthropic Pricing page	Cache Hits $1, 5m writes $12.5, 1h writes $20
reasoning: true	Models page	"Adaptive thinking (always on)" — same as Fable 5
max_input_tokens: 1000000	Models page	1M token context window
max_output_tokens: 128000	Models page	128K max output
multimodal: true	Models page	"All current Claude models support text and image input"

Local Files Inspected

• packages/proxy/schema/model_list.json — confirmed claude-mythos-5 and claude-mythos-preview are both absent; claude-fable-5 exists at line ~7956
• packages/proxy/scripts/sync_models.ts — neither model is in SYNC_EXCLUDED_MODELS or SYNC_PRESERVED_FIELDS

{
  "kind": "missing_model",
  "provider": "anthropic",
  "models": ["claude-mythos-5", "claude-mythos-preview"],
  "status": "active",
  "model_specs": {
    "claude-mythos-5": {
      "format": "anthropic",
      "flavor": "chat",
      "multimodal": true,
      "input_cost_per_mil_tokens": 10,
      "output_cost_per_mil_tokens": 50,
      "input_cache_read_cost_per_mil_tokens": 1,
      "input_cache_write_5m_cost_per_mil_tokens": 12.5,
      "input_cache_write_1h_cost_per_mil_tokens": 20,
      "displayName": "Claude Mythos 5",
      "reasoning": true,
      "reasoning_budget": true,
      "max_input_tokens": 1000000,
      "max_output_tokens": 128000,
      "available_providers": ["anthropic"]
    },
    "claude-mythos-preview": {
      "format": "anthropic",
      "flavor": "chat",
      "multimodal": true,
      "displayName": "Claude Mythos Preview",
      "reasoning": true,
      "reasoning_budget": true,
      "max_input_tokens": 1000000,
      "max_output_tokens": 128000,
      "available_providers": ["anthropic"]
    }
  },
  "source_urls": [
    "https://platform.claude.com/docs/en/about-claude/models",
    "https://platform.claude.com/docs/en/about-claude/pricing"
  ]
}