008How big do OpenAI and Anthropic get by 2027?

The leaks agree with each other

Neither company reports its run-rate on a schedule. The figures arrive through funding announcements, investor updates and leaks, on different dates and sometimes on different definitions. We collected 145 of them. 80 give a run-rate or revenue for a specific period; dropping repeats of the same figure, later restatements and figures on a different basis leaves the 40 we fit. One smooth path through each company’s figures misses the typical Anthropic figure by 3% and the typical OpenAI figure by 1%; the largest miss is 17%. The run-rates, the quarterly revenue and Anthropic’s draft prospectus tell one story.

The OpenAI path implies about $10.1B of revenue in the third quarter, up 50% from the second. OpenAI hasn’t reported it yet.

The curves crossed in the summer

On the fitted path, Anthropic’s run-rate grew about 44% a month in February and 49% in March and was down to about 3% by September; only the third-quarter total pins down how August and September split. Its revenue rose 45% in the third quarter, after 145% in the second. OpenAI went the other way: about 3–4% a month in March and April, 17–19% from July to September. The Information reported that OpenAI’s run-rate grew 70% from the end of June to the end of September, and Bloomberg that enterprise sales were driving most of the growth.

OpenAI followed the rule; Anthropic broke it twice

The simplest forecast is that the next 12 months grow like the last 12. Run at every month-end with only the figures public at the time, it called OpenAI well: its typical miss was 8% four to seven months out and 19–24% further out, on the high side. On Anthropic it missed by about a third four to 12 months out and by 74% beyond a year, on the low side, because Anthropic kept accelerating. Then it broke the other way. Run today, it puts Anthropic at about $174B at the end of 2026, far above the roughly $100–110B in recent reporting.

The version that has growth halving over 18 months did worse than the plain rule beyond three months for both companies, because neither has slowed on a twelve-month view yet. Anthropic has slowed for a few months before: its monthly growth fell from about 40% to about 12% during 2025, then picked up again in early 2026.

OpenAI hit its 2024 revenue plan exactly and its 2025 plans within 3–13%. On its own latest forecast of about $35B, it will beat the 2026 plans it had in 2025 by 17–19% (about 25% on our estimate). Only its earliest pitch was far off: in late 2022 it told investors it would make $1B in 2024, and it made $3.7B. Anthropic’s projections a year out have been too low, mostly by a lot: its 2025 base case was less than half what it booked, and in October 2025 its internal base case for its 2026 run-rate was $20B. Its short-range calls held up: it projected $9B for the end of 2025 and got $9B, and its second-quarter projection was within 6%. Its one miss on the high side was its first: a $200M pace by the end of 2023, against $87M at the start of 2024.

A read on Anthropic, not on OpenAI

Spend on Anthropic’s models through OpenRouter has run at 1.5–2.1% of its revenue each quarter since the end of 2025. Scaling each quarter’s OpenRouter spend by the previous quarter’s ratio would have called Anthropic’s revenue within 12–17% in four of the last five quarters and been 29% off in the fifth (the two 2025 quarters are our estimates from annual revenue). It can’t do the same for OpenAI, whose revenue comes mostly from ChatGPT and from businesses buying directly, which OpenRouter doesn’t see.

The swing factor is Anthropic’s share. It held at 54–62% of OpenRouter’s dollars from January to July, fell to 42% in August as its own spend there dropped, and to 28% in September as OpenAI’s GPT-5.6 and GPT-6 models took share. It recovered to 37% in October after Anthropic released Opus 5.5 and Sonnet 5.5 in late September and Haiku 5.5 in early October. Opus 5.5 alone is drawing more spend than Opus 5 ever did, at lower prices: $4 and $20 per million input and output tokens, against $5 and $25. Revenue moves less than this share does: in August and September, Anthropic’s spend through OpenRouter ran about 30% below July’s while its run-rate kept rising.

Pack 007’s base case has spend through OpenRouter growing 4.2× from October to December 2027. If Anthropic held its October share, that would put its run-rate near $350B; if its share settled at 30%, about $285B; if it kept falling at this year’s pace, about $180B. Our base case of $265B implies a share near 28%, about where it was at its September low.

The forecast

End of 2026. OpenAI expects to reach or exceed a $70B run-rate. It beat its end-2025 target by 7%, and the trend rule says $70B. We use $72B. For Anthropic, October’s spend through OpenRouter implies a run-rate of about $84B at this year’s average quarterly ratio (1.8%), and about $80B if October behaves like June, the last month with a launch-driven jump of the same size. We take $83B. Growth of about 10% a month from there reaches $100B in December, with about $22B of fourth-quarter revenue. That is at the top of what the FT reported after Anthropic’s investor day, an annualized figure below $100B, and short of the $110B analysts said was possible.

2027. For OpenAI we assume its growth rate in December 2026, about 13% a month, halves every 18 months. That gives about $230B in December 2027. For Anthropic we take the midpoint of two methods. The same rule, applied to its growth of about 10% a month late in 2026, gives $245B. OpenRouter gives $285B if Anthropic’s share of spend there settles at 30% while the market follows pack 007’s base case. The midpoint, $265B, is what you get if Anthropic enters 2027 growing about 11% a month and that rate halves every 18 months. The ranges come from varying the year-end level, the starting growth rate and the fade, from halving every 6 months to every 4½ years. On OpenAI’s accounting Anthropic would be about $245B, a little ahead of OpenAI.

For OpenAI, history leans to the upside: a rule that had its growth halving over 18 months ran 23–35% low eight to 18 months out. For Anthropic it cuts both ways: rules built on its trailing growth were far too low until mid-2026 and are far too high now. Scale argues for caution. Each company would add roughly $155–165B of run-rate in 2027, more than either has added in a year so far, and both depend on compute arriving on schedule. Anthropic’s own IPO projection, $190–200B of revenue in 2028, implies about $140B at the end of 2027 if its growth fades as in our base case. It has beaten every longer-range projection it has made since the start of 2025.

What to watch

Anthropic on OpenRouter in November. If spend holds near the $4.5–5M a day it has averaged since October 6, the October jump was real demand and $100B by December looks low. If it falls back by a third or more, as it did in late July, $85–90B is more likely.

OpenAI’s third-quarter revenue. Our fitted path says about $10.1B. Much less would mean the run-rate figures ran ahead of revenue.

Anthropic’s prospectus. If Anthropic goes ahead with its IPO, the public filing should show quarterly revenue on one definition, next to the run-rates it has been quoting.