diff --git a/reddit_api_kernel/connection_state_machine.ml b/reddit_api_kernel/connection_state_machine.ml
new file mode 100644
index 00000000..e69de29b
diff --git a/reddit_api_kernel/connection_state_machine.mli b/reddit_api_kernel/connection_state_machine.mli
new file mode 100644
index 00000000..645722ca
--- /dev/null
+++ b/reddit_api_kernel/connection_state_machine.mli
@@ -0,0 +1,46 @@
+open! Core
+
+module When_to_send : sig
+  type t =
+    | Now
+    | Check_after_receiving_response
+    | After of Time_ns.t
+end
+
+type t [@@deriving sexp_of]
+
+(** {1 Constructors} *)
+val create : rate_limiter:Rate_limiter_state_machine.t -> t
+
+val by_headers : t
+val with_minimum_delay : delay:Time_ns.Span.t -> t
+val combine : t list -> t
+
+(** {1 Events} *)
+
+(* TODO: Move *)
+module Access_token : sig
+  type t =
+    { token : string
+    ; expiration : Time_ns.t
+    }
+end
+
+val send_request
+  :  t
+  -> now:Time_ns.t
+  -> t * [ `Send_it | `Get_access_token | `Wait_until of Time_ns.t ]
+
+val got_access_token : t -> Access_token.t -> t
+
+(** -- *)
+
+(** [sent_request_unchecked] should called immediately after sending a request.
+    It is the caller's responsibility to first call {!wait_until}. *)
+val sent_request_unchecked : t -> now:Time_ns.t -> t
+
+val received_response : t -> Cohttp.Response.t -> t
+
+(** {1 Accessors} *)
+
+val wait_until : t -> When_to_send.t