fix(models): update gpt-5.6 terra/luna pricing

[smakosh]

Summary

OpenAI cut GPT-5.6 Terra and Luna pricing (announcement). This updates all six provider mappings (openai, azure, aws-mantle) in packages/models:

Model	Input	Cached input	Output
Terra	$2.50 $2.00	$0.25 $0.20	$15.00 $12.00
Luna	$1.00 $0.20	$0.10 $0.02	$6.00 $1.20

Cache-write and over-272K long-context tier prices are rescaled from the new bases using OpenAI's unchanged multipliers (1.25× cache write; 2× input-side / 1.5× output over 272K), as enforced by openai-gpt56-pricing.spec.ts.

Also adds a public changelog entry (gpt-5-6-terra-luna-price-cut, id 72) announcing the cuts and linking OpenAI's post, with its OG image generated via gpt-image-2.

Verification

• pnpm build — 17/17 tasks pass (including ui with the new changelog entry)
• openai-gpt56-pricing.spec.ts, validate-model-capabilities.spec.ts, and all packages/models specs pass (139 tests)
• pnpm format — clean, no other surfaces hardcode these prices

https://claude.ai/code/session_014GCx4tQ7GTxcuf92BByQGZ

[coderabbitai]

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Walkthrough

Reduced token and cache-write pricing for gpt-5.6-terra and gpt-5.6-luna across OpenAI, Azure, and AWS Mantle, and documented the new rates and billing behavior.

Changes

GPT-5.6 pricing

Layer / File(s)	Summary
Update GPT-5.6 provider pricing packages/models/src/models/openai.ts	Reduced top-level and tier-specific input, output, cached-input, and cache-write prices for Terra and Luna across OpenAI, Azure, and AWS Mantle providers.
Document new GPT-5.6 rates apps/ui/src/content/changelog/2026-07-30-gpt-5-6-terra-luna-price-cut.md	Added the price-cut announcement, updated rate table, derived pricing details, billing guidance, capability notes, and related links.

Estimated code review effort: 2 (Simple) | ~10 minutes

Possibly related PRs

• theopenco/llmgateway#3191: Modifies the same GPT-5.6 pricing entries and adds Azure mappings.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly summarizes the main change: updating GPT-5.6 Terra/Luna pricing in models.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch update-gpt56-terra-luna-pricing

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[steebchen]

Images automagically compressed by Calibre's image-actions ✨

Compression reduced images by 71%, saving 1.4 MB.

Filename	Before	After	Improvement	Visual comparison
apps/ui/public/changelog/gpt-5-6-terra-luna-price-cut.png	2.0 MB	598.0 KB	71.0%	View diff

[steebchen]

Images automagically compressed by Calibre's image-actions ✨

Compression reduced images by 7%, saving 42.1 KB.

Filename	Before	After	Improvement	Visual comparison
apps/ui/public/changelog/gpt-5-6-terra-luna-price-cut.png	598.0 KB	556.0 KB	7.0%	View diff

[steebchen]

Images automagically compressed by Calibre's image-actions ✨

Compression reduced images by 5.6%, saving 31.0 KB.

Filename	Before	After	Improvement	Visual comparison
apps/ui/public/changelog/gpt-5-6-terra-luna-price-cut.png	556.0 KB	524.9 KB	5.6%	View diff

[steebchen]

Images automagically compressed by Calibre's image-actions ✨

Compression reduced images by 8.6%, saving 45.1 KB.

Filename	Before	After	Improvement	Visual comparison
apps/ui/public/changelog/gpt-5-6-terra-luna-price-cut.png	524.9 KB	479.8 KB	8.6%	View diff