Motivated by LLMs, which generate outputs by iteratively sampling from next-token distributions, we introduce a PAC-learning model for binary stochastic autoregressive learning. This generalizes the deterministic autoregressive learning framework of Joshi et al., COLT 2025. In our model, one fixed generator assigns a Bernoulli next-token distribution to every prompt string. Starting from an input prompt, a token is sampled and appended to the prompt; the same generator is then applied again to this expanded prompt; this procedure is repeated for
M steps. Three forms of supervision are considered: base one-step samples, chain-of-thought (CoT) samples that reveal full random trajectories of length
M, and end-to-end (e2e) samples that reveal only the final token of length
M trajectories. For a generator class, we study the minimum number of samples
mbase(ε),mCoT(ε),me2e(ε), resp., required to learn the one-step probabilities in the base model, and the final-token probability in the CoT and e2e models, under squared loss error~
ε. We show that stochastic autoregressive learning fundamentally differs from the deterministic theory. At scale
ε, there is no universal comparison between the three learning tasks: both
mCoT/mbase and
me2e/mCoT can be made simultaneously arbitrarily larger than
M/ε, the natural analogue for the existing deterministic results. Nevertheless, after altering scales, for every class, CoT learning at scale
ε is upper-bounded by base learning at scale
ε/M2, whereas e2e learning at scale
ε is upper-bounded, up to logarithmic factors, by
(M/ε)mCoT(Θ(ε)). These dependencies and scales are essentially tight. We complement these bounds by studying dimension
d logistic functions in our model.