diff --git a/api/services/control/control.proto b/api/services/control/control.proto
index 20099aa65..0d20cc7b4 100644
--- a/api/services/control/control.proto
+++ b/api/services/control/control.proto
@@ -2,6 +2,9 @@ syntax = "proto3";
 
 package moby.buildkit.v1;
 
+// The control API is currently considered experimental and may break in a backwards
+// incompatible way.
+
 import "github.com/gogo/protobuf/gogoproto/gogo.proto";
 import "google/protobuf/timestamp.proto";
 import "github.com/moby/buildkit/solver/pb/ops.proto";
diff --git a/frontend/gateway/pb/gateway.proto b/frontend/gateway/pb/gateway.proto
index e7cf38240..0e92f1302 100644
--- a/frontend/gateway/pb/gateway.proto
+++ b/frontend/gateway/pb/gateway.proto
@@ -12,8 +12,11 @@ option (gogoproto.marshaler_all) = true;
 option (gogoproto.unmarshaler_all) = true;
 
 service LLBBridge {
+	// apicaps:CapResolveImage
 	rpc ResolveImageConfig(ResolveImageConfigRequest) returns (ResolveImageConfigResponse);
+	// apicaps:CapSolveBase
 	rpc Solve(SolveRequest) returns (SolveResponse);
+	// apicaps:CapReadFile
 	rpc ReadFile(ReadFileRequest) returns (ReadFileResponse);
 	rpc Ping(PingRequest) returns (PongResponse);
 }
@@ -33,6 +36,8 @@ message SolveRequest {
 	string Frontend = 2;
 	map<string, string> FrontendOpt = 3;
 	repeated string ImportCacheRefs = 4;
+	
+	// apicaps.CapSolveInlineReturn deprecated
 	bool Final = 10;
 	bytes ExporterAttr = 11;
 }