The week after DevDay, the group chat is not “Astra won.” It is three console screenshots stacked together: OpenAI’s Agents API, Anthropic’s Fable cache price, Google’s Flash promo countdown. The same “add an export to the admin” ticket gets a $10/$50 paste from one person and $0.75 from another. Finance asks whether the month-end bill will differ by an order of magnitude.
The model page, the agent page, and the seat page are often three invoices. For how the product shells split, see Claude Code vs Codex vs Gemini 3.8 Flash; for Astra’s own wall-clock and tokens, see how strong GPT-6 Astra is at coding. Below is only the API: price, speed, agent capability—and why those three cannot be read alone.
After this wave, which invoices is the API comparing
September 2026 stacked at least this much in public: gpt-6-astra on the API plus Azure / Bedrock; the Agents API in public beta on 10 September (hosted Codex harness, no extra interface fee, billed on tokens and tools); Anthropic cutting Fable 5.1 cache reads to $0.25; Gemini 3.8 Flash hanging its intro price through 2026-12-31. The Agent Builder canvas is scheduled to shut down on 30 November—migrate to the Agents SDK.
Do not start with “who is smarter.” Line up the invoice shape first:
| Ledger | OpenAI | Anthropic | |
|---|---|---|---|
| Model API | Astra / Sol / Terra by token | Fable / Opus / Sonnet by token | Flash by token (seats billed separately) |
| Cache | Read $1, write $12.50; whole-request surcharge past 272K | Fable 5.1 reads $0.25 | Caching supported; still far below flagship list |
| Agent runtime | Agents API: sandbox, MCP, compaction, sub-agents | Claude Code / Messages tool loop | Antigravity, Managed Agents |
| Extras | Computer use per tool call; Fast about ×2 | Opus Fast (preview, not Fable) | Thinking level and tool rounds lift tokens |
Figures align with September 2026 public list prices. FX, tax, and promos move—recheck the vendor page before you buy.
Is list price the same as cost per finished task
Per million tokens (input / output):
| Model | Input | Output | Cache read | What to read first |
|---|---|---|---|---|
| Gemini 3.8 Flash (through 2026-12-31) | $0.75 | $3.75 | Far below flagship | $1.50 / $7.50 from 2027-01-01 |
| GPT-5.6 Terra | $2 | $12 | — | Everyday Codex / API tier |
| Claude Sonnet 5 | $2 | $10 | 0.1× input | Default starting point for most coding |
| GPT-5.6 Sol | $4 | $20 | — | Previous flagship |
| Claude Opus 5 | $5 | $25 | 0.1× input | Anthropic: “start here for most work” |
| GPT-6 Astra | $10 | $50 | $1 | Past 272K: input/cache ~×2, output ~×1.5; Fast ×2 |
| Claude Fable 5.1 | $10 | $50 | $0.25 | 5-minute cache write $12.50; 1-hour write $20 |
A mid-size turn at 80k in + 8k out is roughly $0.09 on Flash, $0.24 on Sonnet, $0.26 on Terra, $0.48 on Sol, $0.60 on Opus, $1.20 on Astra / Fable. Agents rarely fire once. Cache hits, thinking knobs, and tool rounds split “cheap per token” from “cheap per ticket.”
Flash’s intro rate is about one-thirteenth of the flagship sticker. That is not “free Claude.” Google is explicit: on hard work, 3.8 takes extra reasoning steps and tool rounds. A cheap brain plus dense tools can still land near a mid-tier model on tokens. For stacking subscription, API, and a machine on one month, see how much an AI coding agent costs per month.
Where wall-clock speed actually lives
All three hide “faster” in knobs, not in the model name.
- Astra:
reasoning.effortis low / medium / high / xhigh / max (nonone). Higher effort likes more rounds and browser checks. API Fast is about 2× wall clock and 2× list price. On the launch page, OSWorld 2.0: Astra about 72.6% / 40 minutes, Sol about 65.7% / 75 minutes. - Fable 5.1: the official table is slower than Opus 5 and Sonnet 5; thinking is adaptive and defaults to
high. You are buying long-horizon judgment, not first token. - Flash: Flash-class first byte; thinking low / medium / high (
minimalerrors). Daily work at low effort drops clock and tokens together; on hard tasks it adds rounds on its own.
A fast first token is not a finished ticket. Astra more often greens the queue and CI first, then needs a second pass on empty states; Fable more often saves a UI and risk-note rewrite. For the same project head-to-head, see GPT-6 Astra vs Claude Fable 5.1 on the same project.
Agent capability: split the model, the shell, and the hosted runtime
Picking an API in 2026 means at least three layers:
- Model: does it change the right files, stay in scope, and avoid blowing the repo into context.
- Shell: Codex, Claude Code, Antigravity—defaults for permissions, sandbox, MCP, and sub-agents differ.
- Hosted runtime: the Agents API hangs the Codex harness on one HTTP call; you pick a sandbox or your own box, OpenAI runs orchestration, compaction, and recovery. No extra interface fee; computer use and similar tools bill separately.
OpenAI adds two bits of friction: tool calling needs the Responses API (Chat Completions is not enough); production misalignment monitoring can stop an API task outright, not just ask for confirmation. Astra’s computer use looks strong on Agents' Last Exam and OSWorld—forms, CRM, browser QA. Cyber capability hits Critical: defensive review is in; advanced exploit-style asks are refused.
Claude’s remaining edge is still MCP + cache economics + long-horizon caution. Gemini’s is cheap throughput + managed agents, but Code Assist / Enterprise seats are a second line on the invoice. Wiring Flash into a multi-backend shell like Codex is the usual “cheap brain + mature loop.”
# A common split for one ticket (not the only split)
Flash / Terra / Sonnet → probe, tests, read-only repo sweep
Sol / Opus → change a public API, close the diff
Astra / Fable 5.1 → cross-module, overnight, artifacts or cache
Agents API / Claude Code → hosted only when you need sandbox + resume
Match the task; do not pick a camp
| What you are doing | API tier to try first |
|---|---|
| Batch shorts, multimodal, doc sweeps | Gemini 3.8 Flash, thinking=low |
| Daily API edits, tests, PR close-out | Sonnet 5 or Terra; Sol / Opus when needed |
| Cross-module refactors, overnight agents | Fable 5.1 (cache) or Astra (computer use / professional docs) |
| Browser forms, desktop ops, site QA | Astra + Responses / Agents API |
| A bill you can forecast | Cheap default + monthly API cap; a subscription hits a wall and stops, an API hits a wall and charges |
A few things that do not fit a comparison table and still punch through a budget:
- Already paying ChatGPT Plus / Claude Pro, then opening an uncapped API for the same agent, is double-counting.
- Astra Fast + past 272K multiplies; a large window is not a license to paste the repo.
- Agent Builder workflows need to move to the Agents SDK before 30 November. Do not treat the canvas as a long-term architecture.
- Mixing is often cheaper than picking a side: one shell for hard bugs, Flash for throughput, a cache-friendly flagship overnight.
FAQ
Astra and Fable 5.1 have the same sticker. Can I just pick either?
Same sticker, different second read of context. On long sessions and repeated repo sweeps, look at cache reads first. If you need computer use, professional artifacts, or the Codex / Agents API harness, look at Astra.
Can Gemini 3.8 Flash be the production default?
It can be the throughput default, especially through the end of 2026. On hard tasks it adds rounds itself, so a single task is not always cheapest. The terminal loop, permissions, and MCP still need a shell. Personal Code Assist has tightened—do not budget from the 2025 free-tier memory.
Should we move to the Agents API now?
If you want a cloud sandbox, session resume, and no harness to keep alive, a pilot is worth it. There is no extra interface fee, but tokens, tools, and a monitor that can stop a task all count. Long-horizon work already smooth in Claude Code does not have to relocate because DevDay shipped a new API.
A cheap API still needs a machine that stays open
Tokens are billed in the cloud; the repo, tests, MCP, and sandbox run on the box in front of you. Close the laptop and the session dies, the prompt cache expires, and “continue” is billed as a full input—Astra also surcharges the whole request past 272K. A Mac mini idles around 4W, so the agent can work against your rolling window instead of rebooting with the lid.
Apple Silicon unified memory is a better fit for indexing a large repo and running tests in parallel; macOS ships Unix, Homebrew, Docker, and SSH, so Codex, Claude Code, and a self-hosted Agents loop skip a WSL layer. Against a same-price Windows box you get fewer crashes, stabler unattended runs, and Gatekeeper plus SIP for a machine that stays up with an agent on it.
If you are already shaving list prices and cache across three APIs, keeping the machine awake is often a better buy than one more flagship tier—see the plans and spend the money on changing code, not on warming up again.