On August 31 Claude Sonnet 5 jumps from $2 to $3 per million input tokens with a tokenizer change, while GPT-5.4 and mini leave Codex. Two migrations hit…
Mark August 31 on your calendar, because it's the rare day where two of the biggest AI cost changes land at the same time and pull in opposite directions.
Claude Sonnet 5 moves from $2 to $3 per million input tokens and $10 to $15 per million output tokens, alongside a tokenizer change that adds anywhere from 10 to 35 percent more tokens on code. On the same day, GPT-5.4 and GPT-5.4 mini leave Codex for ChatGPT sign-in users, though both stay available through the API.
The Repricing Hiding Inside a Price Hike #
The Sonnet 5 change isn't a simple bump. A tokenizer change means the same code you wrote before now consumes more tokens to represent, so the effective cost increase is bigger than the headline dollar move. If your code tokenizes 20 percent heavier and the price rises 50 percent, your real cost per line of code goes up by more than the sticker suggests.
That's the kind of detail that quietly ruins a quarterly cloud budget. The list price going from $2 to $3 is easy to understand. The tokenizer silently inflating the denominator at the same time is the part teams miss until the invoice shows up.
The Migration on the Other Side #
Over at OpenAI, GPT-5.4 and GPT-5.4 mini leave Codex, the coding product, for ChatGPT sign-in users. The framing matters: this is a product access shift, not a model shutdown, because both models stay available via API key. But if your developers were using Codex as a convenient front-end, they're now being nudged to a different entry point at the exact moment Anthropic is making the alternative more expensive.
For teams running coding workloads across both platforms, next Monday is a repricing and a migration at once. That's a genuinely awkward position to be in, and it's not an accident of the calendar. Pricing and product-access changes have a way of clustering around fiscal boundaries, and both of these land on the last day of the month.
What to Actually Do #
First, re-baseline your token counts on Sonnet 5 with the new tokenizer before you assume you know the cost. A spot check on real code, not docs, is the only number that matters. Second, map which of your Codex users actually need Codex versus which just need an API key and a lighter interface. Third, remember the wider context: GPT-5.6 Sol is on promotional pricing until around November 21, at $4 in and $20 out, before returning to $5 and $30.
The ones who get squeezed are the teams that did nothing. The frontier labs have been raising prices on the rails they control while dangling cheaper promotional alternatives to move you. You can't avoid the repricing. But you can decide whether you get caught flat-footed or walk into it with your numbers already done.
Sources: Anthropic pricing update, August 2026; OpenAI Codex access change, August 2026; AI Tools Recap deadline tracker, August 23, 2026.
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