Cracks in the AI Thesis

Dear Colleagues: Today’s letter includes my monthly update of Ramp AI Index, our flagship research using spend data from Ramp to track how American businesses are using AI. In this post, I cover the latest on business adoption of cheaper, open source models and a lookback on Anthropic’s Fable launch, why business takeup has been slower than expected, and what that means for the AI trade.

Model market share: Anthropic, xAI gain. OpenAI underperforms.

In July, Anthropic extended its gains as the leader in business AI adoption. 43.5% of U.S. businesses paid for subscriptions or tokens from Anthropic, up 1.1 percentage points month-over-month. xAI posted its fastest growth since July 2025, rising 0.94 percentage points to 4% of businesses. OpenAI underperformed overall AI adoption, rising only 0.23 percentage points to 39.7% of businesses.

Our latest data shows businesses are hitting their limit on AI spend

These charts that make me wary about the AI trade – all from Ramp spend data.

The share of businesses using model serving platforms, which provide access to open source models and some Chinese-developed models, rose again last month. 6.1% of businesses using AI are now using these platforms, up 0.2 points from last month. I previously wrote about how this growth has yet to meaningfully impact spending on OpenAI and Anthropic.

But adoption of OpenAI and to a lesser extent, Anthropic, has slowed in recent months. That’s not because new AI spenders are switching to open source / Chinese models (they most definitely are not doing that — first-time buyers on AI are still using the American model companies). But it means more of their growth will have to come from existing businesses spending on AI, particularly the advanced spenders, and those businesses are increasingly spending on open source.

Meanwhile, last month, Anthropic released the best AI model to ever hit the market, Fable 5, and we now have the first public data to share business uptake of the model so good its release was briefly blocked by the U.S. government: one month in, businesses aren’t using it that much.

Over the last month, Fable 5 has made up only 6% of tokens businesses purchased from Anthropic, and despite being their most expensive model by far, 11.4% of dollars spent on Anthropic models.

For comparison, OpenAI’s flagship model, GPT-5.6 Sol, comprises 25% of OpenAI tokens and 23% of spend. In fact, Fable 5 is less popular with businesses than GPT-5.6 Sol overall. In July, Fable 5 generated approximately 75% as much model-attributed spend as GPT-5.6 Sol.

So why does this make me wary of the AI trade? Fable 5 is the most performant model on the market. It’s also the most expensive, at roughly $10 per 1M tokens, twice as expensive as the still highly performant GPT-5.6 Sol.

So with Fable 5, we’ve found a new upper bound for how much businesses are willing to spend on AI. Here, more performance is not worth the price tag. To encourage business adoption of the latest models, the labs will need to prove performance beyond what even Fable 5 is able to achieve and simultaneously ensure that competitors aren’t able to come reasonably close. That seems increasingly out of reach, especially as open source models catch up to being only a few months behind.

Note on our methodology: the data for this chart on Fable usage is sourced from Ramp’s token spend management product, which allows us to track daily usage data on token usage by firms. The sample of businesses here skews slightly more tech-y than our typical AI Index sample. So actual Fable adoption is likely even lower than what we have estimated here. As always, this data is anonymized and aggregated so that no one business is identifiable in our research.

And here’s some reprieve. Despite these competitive pressures that are driving down the cost of AI, American companies continue to ramp AI spend. In July, the top 1% of businesses spent a median $7,400 per employee on AI. The top 10% spent $650. The median firm spent $11.95 per employee.